Fulvic and humic acids have been studied for decades and used extensively in the soil and hydroponic growing industries. I previously talked about the use of humic acid in hydroponics and the way in which it can improve crop results. In that post, we talked about how humic acids can improve nutrient chelation and how this can lead to improvements in yields depending on the origin and properties of the humic substances used. In this post, we are going to take a look specifically at fulvic acid substances, which are a smaller family that has potentially more valuable uses in the hydroponic space. We will start by discussing what differentiates fulvic and humic acids and what the current peer-reviewed evidence around fulvic acids tells us.

Fulvic acids are not chemically pure substances, but a group of chemicals that result from the decomposition of organic matter. This process generates both humic and fulvic acids. However, fulvic acids are different from humic acids in mainly two ways. The first is that fulvic acids are soluble at both acid and alkaline pH values, and the second, is that fulvic acids generally have much lower molecular weights. Fulvic acids are therefore more soluble and are more easily accessible to plants compared to humic acids, which have much larger molecular weights. But why should we use them in hydroponics and exactly how?

Sadly, not many publications have tackled the use of fulvic acid in crops specifically. One of the few examples of reviews that touch on the matter is this paper, which covers most of the literature around fulvic acids before 2014. I also did a literature review myself, trying to find articles in which the fulvic acid source, application type and rate, and the results against a control without fulvic acid were clearly explained. The table below shows you the results of my search, I was able to find 10 papers overall, with a mix of root and foliar applications of fulvic acid, with a range of application rates and plant species. Almost all of these papers found positive results from the use of fulvic acid, except two papers that found either no effect or mixed results from their use.

The range of application depends substantially on the application type. Most papers that tackled foliar applications chose application rates in the 1-3g/L range, while papers that tackled root applications generally stayed in the 25-150ppm range. This is normal since foliars are generally much more concentrated than root applications. Both types of applications have different effects. Root applications are going to exercise an additional strong nutrient chelating role, while foliar applications are more likely to exert a hormonal role. A study around genetically modified tomato plants showed that plants engineered to be insensitive to IAA were also unable to respond to fulvic acid, hinting at the fact that fulvic acid has an auxin-like effect in plants.

The effects seem to be quite positive overall, with increases in yield, quality, and flower numbers across the board. The studies above that investigated nutrient transport also showed substantial benefits when root applications of fulvic acid were used. Plants grown in a Hoagland solution showed better nutrient transport when fulvic acid substances were used in the nutrient solution. This is possibly both due to their ability to chelate micronutrients and their ability to provide an additional pH buffer at the region of interest in hydroponics (5.5-6.5). This study, shows how fulvic acid substances can have pKa values in this precise region, although their still relatively large molar mass implies that they will contribute marginally to buffering capacity, especially if used only in <100 ppm concentrations.

Fulvic acids also seem to be synergistic with several other biostimulants in the studies showed above. When tests were done with humic acids or other biostimulants, the effect of the combination is usually better than the effect of either part on its own. This means the fulvic acid might not only be a good addition on its own, but it might also contribute significantly to enhance the effect of other biostimulants used.

It is however important to note that fulvic acids do have negative effects when used in excess, reason why their application rates need to be carefully controlled. Using too much can lead to drops in yields and quality along with slower growth. If you want to start using them, it is, therefore, wise to start at the lower range of the application rates shown above and climb up as you gauge the effects. It is also important to note that – as humic acids – different sources of fulvic acid might have different effects, as the actual molecules that make up the substance will change.

A big advantage of the use of fulvic acids in hydroponics is also that their solubility is quite high, so the risk of clogging or damaging equipment is low. This is a significant advantage over humic acids, which have lower solubility and can cause problems because of this in hydroponics culture, especially if there are drops in the pH. In hydroponics, fulvic acids can also lead to additional solution stability, especially in recirculating systems, where the destruction of heavy metal chelates as a function of time can become a bigger risk.

All in all, fulvic acids represent a relatively cheap addition to a hydroponic regime that has limited risk and a lot of potential upsides. Literature research shows us that low rate applications, if anything, might just have no effect, so the risk of damage to a hydroponic crop by trying fulvic acid applications is low. The synergistic effects shown by fulvic acid are also interesting since this means that they might make other additives you are currently using even more potent. When looking for fulvic acids, make sure you check for high solubility, solubility in low and high pH, and a source that matches the sources used in the literature results you’re interested in reproducing.

Although hydroponic crops cannot usually be labeled as “organic” by official certifying authorities, like the USDA, we can create a hydroponic crop that is “organic” in spirit. We can do this if we avoid the use of traditional synthetic chemical fertilizers – meaning using only OMRI listed products – and use a growing media that mimics some of the functionality that is provided by soil. This can be quite tricky to do and can lead to substantial issues in crops, reason why it is important to be aware of the problems that can arise. In this post, I will talk about five important things to consider when trying to do an organic hydroponic crop.

The media needs to be friendly for microbes. A traditional hydroponic crop will benefit from having media that is as inert as possible. However, if you are going to be avoiding synthetic fertilizers, this means that certain functions will need to be carried out by microbes. Most importantly, microbes will carry out the conversion of protein-derived nitrogen to ammonium and then nitrate nitrogen. Peat moss and coco can be friendly media for microbes, while rocky media like rockwool, perlite, vermiculite, and sand, can be more hostile. Peat moss is my preferred media for this type of setup, as the acidification of the peat moss will also help deal with some of the chemical issues that arise through an organic hydroponic crop.

Provide a nutrient solution that is as complete as you can. Your hydroponic nutrient solution should still give your plants a fair amount of nutrition, especially nutrients that are easily soluble and can leech from the media. There are several OMRI approved soluble sources of vegetable/animal-derived nutrition that can be used to create an organic feed for your plants, such as fish emulsions and kelp extracts. There are also some valuable mineral sources that are mined that can be used, such as sodium nitrate, potassium sulfate, gypsum, and magnesium sulfate (Epsom salt). Use these sources to create a balanced nutrient solution for your plants.

Amend the media to compensate for what the nutrition solution will lack. An organic hydroponic crop will generally need to contain some form of amended media because the nutrient solution will not be able to effectively provide all the nutrients it provides in a regular hydroponic crop. The absence of synthetic salts implies that we will not be able to provide things like nitrates and phosphates in the amounts we would desire. This means that nitrogen and phosphorus will both need to be added to the media to some extent. This can be done with vegetable protein, bone meal, and rock phosphate amendments.

Keep aeration higher than you would in a normal hydroponic crop. In a normal hydroponic crop, the number of microorganisms and organic decomposition reactions in the media will be quite low. However, when we move to a setup where a significant amount of nutrition is provided by microorganisms in the root zone, aeration becomes a big issue due to the increased oxygen demand from the bacterial and fungal populations in the media. A media used for an organic hydroponic setup will usually require a substantial amount of aeration to be present. If using peat moss, it is useful to mix it 40/60 with something like perlite or rice husks in order to improve the aeration properties of the media substantially.

Bad heavy metals are going to be your enemy. Plants require some heavy metals and media like peat moss will lack the amounts necessary to properly sustain plant growth. However, resist the temptation to amend the media with something like green sand or azomite – a volcanic rock – as these sources can contain very important amounts of bad heavy metals, like lead, arsenic, and mercury. Instead, it is better to use amendments that provide animal sources of metals – like blood meal – or to use an organic source of soluble heavy metals in your nutrient solution, such as the Biomin series of products. Compost teas can also be a very important source of needed heavy metals. Be very aware of bad heavy metals in your organic inputs.

Inoculate the media with the bacterial and fungal populations you need. Since bacteria and fungi are going to be your allies, you need to properly inoculate the media with healthy microbe populations. I would advise inoculating with both beneficial fungi, like Trichoderma species and also with a bacteria-containing product, such as Tribus. Compost teas can also be an important source of bacteria and fungi to colonize the plant’s rhizosphere.

Although the above is by no means a complete list, it does highlight some key points when moving from a purely hydroponic setup into a hydroponic setup that will rely heavily on microbes for the release of nutrients. This is a midway approach between a soil-based approach and a complete hydroponic setup, where we are expected to provide some of the nutrition through the nutrient solution but a lot of it is also expected to come from the media itself. It can be done successfully and amazing crops can be grown with it, however, it does require you to apply the skills of both soil and hydroponic crop manager.

There has been a battle raging during the past decade between soil-based organic producers and hydroponic growers, to figure out whether hydroponically produced crops can or cannot be considered for organic certification. The entire discussion centers around whether a hydroponically grown crop can in fact comply with the requirements of the USDA organic standard. Within this post, we are going to discuss why there is even a discussion, why a hydroponic crop could be considered organic, and what the arguments against such a designation currently are.

All that is required for a crop to be considered “hydroponic” is the complete absence of soil. This means that all the nutrition required for the crop is going to come from the nutrient solution and the substances that are put within this solution can or cannot comply with the USDA requirements for the “organic” label. Some substances like heavy metal chelates, potassium phosphates, and most nitrates, are forbidden by the USDA organic designation due to their synthetic origin, and the environmental impact of their production and normal usage. However, the total impact of these substances also rests heavily on how the hydroponic crop manages them and how efficiently they are used.

A hydroponic crop could use a fraction of the water and fertilizer used by a traditional soil crop of the same area while capturing all fertilizer effluents, making it environmentally more sustainable than a traditional soil crop and probably worthy of some sort of designation to recognize this fact. A hydroponic crop grown with traditionally produced synthetic fertilizers, that has absolutely no fertilizer dumping of wastewater to the environment and uses no synthetic pesticides on products has a low environmental impact and produces food of very high quality. Hydroponic crops can also use land that would otherwise be unusable by traditional soil-based methods, expanding the area that could be used for healthy and sustainable food production.

However, the defendants of the organic designation argue that it is not only about what is being produced and how it is being produced but where it is being produced. The argument is that the organic designation and requirements have specific provisions about soil sustainability and soil building, that a hydroponic crop could not possibly comply with. They argue that part of the spirit of the organic designation is to make growing in soil more sustainable and that hydroponically grown crops simply cannot do this because they completely lack any soil or any soil building process.

Both hydroponic and traditionally designated organic crops can produce food that is healthy, pesticide-free, and sustainable. Hydroponic crops can do this on land that is not traditionally arable and can do so at astonishingly high efficiencies. Therefore, it would be fair to provide hydroponic crops that are evaluated to be sustainable and grown over non-arable land, an organic designation, since they comply with the spirit of what, I believe, the people who buy organic want, which is to have foods that are produced in a sustainable manner, with little impact on the environment. If the use of synthetic fertilizers is a concern, a requirement to meet this designation could also be the use of the same array of inputs available to traditional organic growers. This is harder to achieve, but still viable within the hydroponic production paradigm.

Recently, hydroponic growers have won battles in California about being granted an organic designation, however, because of the large amount of money that the organic designation carries – allowing growers to charge a big premium for items designated as organic – the organizations of soil-based organic growers are going to continue to fight this as much as they can. Organic grower organizations have even fought the potential for an independent “organic hydroponic” designation (see here), as they say, this might be confused with the normal “organic” designation and negatively affect their products.

Not all hydroponic crops are environmentally sound though. Many of them can be incredibly polluting and can make inefficient use of both water and fertilizer resources. For this reason, a designation is required to distinguish those that are sustainable from those that are not. If the USDA organic designation requirements are adjusted to accommodate for the potential for highly sustainable hydroponic crops grown on non-arable land, this would be a huge step in giving customers a clear way to tell products apart.

Hydroponic crops can be sustainable, have a low impact, and produce very high-quality, nutrient-rich food with no pesticides. They can make more efficient use of land, water, and non-synthetic fertilizers than soil-based crops do. However, the fact is that few of them really meet these criteria, because there is no designation they can achieve that would make this worthwhile from a commercial perspective. So while they are not organic at the moment, giving them the possibility to be organic would be a huge step towards a more sustainable future in agriculture. It could motivate hydroponic growers to become more sustainable and embrace a lot of the practices of soil-based organic growers.

Today I am releasing a new version of HydroBuddy (v1.9) which contains many suggested and needed improvements from the previous version of the software. In this post I want to discuss the changes within this release and how they will affect the way things are done in the program. Some big changes have been implemented so make sure you go through the list below if you want to use this new version. Thanks to all of you who contributed your suggestions about HydroBuddy and/or reported bugs to me.

Here is the list of changes in this version:

• A MacOS binary compiled in Big Sur 11.0.1 has been released.
• Ability to make any formulation the “default” formulation. This selected formulation is loaded when the software is started.
• The LMC conductivity model has now been replaced with LMCv2 which is an important improvement. See here to learn more. The LMCv2 model now adjusts conductivity based on each specific ion’s charge and the overall ionic strength of the solution. It now includes no arbitrary terms.
• The treatment of liquids/solids in the program has now been changed. Instead of specifying liquid or solid (and the program having to make assumptions) users can now select whether the percentages and substance amounts are going to be either in g and w/w% or in mL and w/v%. This should simplify the interpretation of results and the addition of substances.
• An additional column has now been added in the results page to specify the unit of the amount being calculated. When a user wants a substance’s contribution to be calculated in mL, the appropriate unit will be shown here.
• When adding a new substance, all fields are reset to null values (previously the program kept the values from previously opened/updated substances).
• Density has now been eliminated as a variable used in the program since it is not needed if there is no cross between w/w% and w/v% calculations. It is only kept in the “Copy commercial nutrient formulation” dialogue.
• An error where P and K were mixed up in the product comparison window of the “Copy commercial nutrient formulation” function has now been fixed.
• The wording of options in the “Substance selection” dialogue has been changed so that the buttons better describe what they do. For example the “Delete” button has now been changed to “Do not use”.
• Two buttons have been added next to the EC model prediction in order to allow users to increase or decrease the EC by adjusting all nutrient concentrations by +5%/-5%. This will allow you to see how nutrient concentration changes affect conductivity in a straightforward manner.

The above modifications are now committed to the github repository as well. Feel free to take a look if you’re interested in how any of the above variations were coded into the program.

Hydrobuddy’s theoretical conductivity estimates have never been good. As I discussed in a previous post, the program uses a very simple model based on limiting molar conductivities to calculate the EC. The software knows how much each ion conducts when it’s all by itself, so it adds all these conductivity values multiplied by the concentration and assumes there are no additional effects. The conductivity values resulting from this assumption are very large – because there are effects that significantly reduce the conductivity of ions at larger concentrations – so HydroBuddy just cuts the estimation by 35% hoping to reach more accurate values. This works great for some cases, but very badly for others.

The reason why this happens is that the actual conductivity contribution of some ions decreases more drastically as a function of concentration and due to the presence of other ions compared to others. This means that we need to account for these decreases in conductivity in an ion-specific way. One way to approach this, is to forget about theoretical approximations and just create an empirical model that uses experimental data. This is what I did when I created the empirical model that is present in HydroBuddy from v1.7. This model works really well, provided you are using the exact list of salts that were used to create the model and you stay within the boundaries of concentration values that were used to create it.

This experiment-based solution can be great. It is in fact, a technique I’ve used to create custom versions of HydroBuddy for clients who want to have high accuracy in their EC estimations within the salts that they specifically use. The process is however cumbersome and expensive, my wife and I – both of us chemists – do all the experimentation, and it generally requires an entire day, preparing more than 80+ solutions using high accuracy volumetric material, to get all the experimental data. It is also limited in scope, as any salt change usually requires the preparation of a substantial number of additional solutions to take it into consideration.

It would certainly be great if we could create a better, fully theoretical, conductivity model. Diving into the literature and programs used for conductivity-related calculations, I found a program called Aqion that implements a more accurate model compared with HydroBuddy’s LMC model. You can read more about their approach here. They use the limiting molar conductivities but introduce additional terms to make ion-specific corrections that are related to both ionic charge and ionic strength. The ionic charge is the electrical charge of each ion, for example, +1 for K⁺ and +2 for Fe⁺², etc. The ionic strength is the sum of the molar concentration of each ion times its charge.

The plot above shows you how this correction factor affects a solution as the ionic strength and charge of the ions change. As a solution gets more diluted, the equation approaches the sum of the conductivities at infinite dilution. Conversely, as the solution becomes more concentrated or the ion charge becomes higher, the drop in the conductivity becomes more pronounced. These are both phenomena that are in-line with experimental observations and much better reflect how conductivity is supposed to change when different ions interact in solution.

The above equation provides us with a more satisfactory theoretical estimation of conductivity compared to the current HydroBuddy LMC model. The new model is able to implement correction factors on a per-ion basis and also changes the magnitude of these corrections depending on how concentrated the solutions are. This new model will be implemented to replace the current LMC model in HydroBuddy v1.9, which will be released in the near future. This should provide significantly more accurate estimates of conductivity for the preparation of hydroponic solutions.

There are multiple open-source projects available online for the creation of pH/EC sensing stations for hydroponics. However, all of the ones I have found use a single Arduino or Raspberry Pi to perform the measurements and store any data, making them unsuitable for applications where more flexibility is needed. For example, a facility using multiple different reservoir tanks for nutrient storage might require multiple pH/EC sensing stations, and single-board wired setups would be unable to accommodate this without a lot of additional development. In this post, I am going to show you a simple pH/EC sensing station I built with an Arduino MKR Wifi 1010 that can communicate with a MyCodo server using the MQTT protocol. Multiple sensing stations could be built and all of them can communicate with the same MyCodo server.

This project makes use of the small pH/EC boards provided by uFire, which have a lower cost compared to those provided by companies like Atlas, but do have adequate electrical isolation to avoid problems in readings when multiple electrodes are put in the same solution. This is a substantial improvement over other low-cost boards where using multiple probes can cause heavy electrical noise and interference. In order to build this project you will require the following materials:

Note, some of the links below are amazon affiliate links. This means that I get a small commission if you purchase through these links at absolutely no extra cost to you. The links to other websites are not affiliate links.

1. Arduino MKR Wifi 1010
2. uFire pH probe
3. uFire EC probe
4. A rugged pH probe with a VNC connector
5. An rugged EC probe with a VNC connector
6. Two Qwiic-to-Qwiic connectors
7. One Qwiic-to-male connector
8. A project box to put everything inside (optional)
9. A micro USB cable

The code for the project is shown below:

#include <uFire_EC.h>
#include <uFire_pH.h>
#include <WiFiNINA.h>
#include <ArduinoMqttClient.h>

#define SECRET_SSID "ENTER WIFI SSID HERE"
#define SECRET_PASS "ENTER WIFI PASSWORD HERE"

//calibration solutions used
#define PH_HIGH_SOLUTION_PH 7.0
#define PH_LOW_SOLUTION_PH  4.0
#define EC_HIGH_SOLUTION_EC 10.0
#define EC_LOW_SOLUTION_EC  1.0
#define CALIBRATION_TEMP    20.0

// topics for the mqtt sensors
// Make sure all stations have different topics
#define EC_TOPIC       "EC1"
#define PH_TOPIC       "PH1"
#define CALIB_TOPIC    "CALIB1"
#define MQTT_BROKER    "ENTER MQTT SERVER IP HERE"
#define MQTT_PORT      1883

int status = WL_IDLE_STATUS;     // the Wifi radio's status
String message;

uFire_pH ph;
uFire_EC ec;
WiFiClient wifiClient;
MqttClient mqttClient(wifiClient);

void check_connection()
{
  if (!mqttClient.connected()) {
    WiFi.end();
    status = WiFi.begin(SECRET_SSID, SECRET_PASS);
    delay(10000);
    if (!mqttClient.connect(MQTT_BROKER, MQTT_PORT)) {
      Serial.print("MQTT connection failed! Error code = ");
      Serial.println(mqttClient.connectError());
      delay(100);
    }
    mqttClient.subscribe(CALIB_TOPIC);
  }
}

void setup()
{
  Serial.begin(9600);
  while (!Serial);

  // connect to wifi and mqtt broker
  check_connection();
  
  // coorectly initialize the uFire sensors
  // note the Wire.begin() statement is critical
  Wire.begin();
  ec.begin();
  ph.begin();
}

void loop()
{
  // mqtt keep alive
  mqttClient.poll();

  // read messages 
  message = "";
  while (mqttClient.available()) {
      message += (char)mqttClient.read();    
    }

  // execute calibration if requested
  Serial.println(message);
  if (message == "EC1_HIGH") ec.calibrateProbeHigh(EC_HIGH_SOLUTION_EC, CALIBRATION_TEMP);
  if (message == "EC1_LOW")  ec.calibrateProbeLow(EC_LOW_SOLUTION_EC, CALIBRATION_TEMP);
  if (message == "PH1_HIGH") ph.calibrateProbeHigh(PH_HIGH_SOLUTION_PH);
  if (message == "PH1_LOW") ph.calibrateProbeLow(PH_LOW_SOLUTION_PH);

  // Measure EC 
  ec.measureEC();
  Serial.println((String) "mS/cm: " + ec.mS);

  // Measure pH
  ph.measurepH();  
  Serial.println((String) "pH: " + ph.pH);

  // Ensure the wifi and mqtt connections are alive
  check_connection();

  // post EC to MQTT server
  mqttClient.beginMessage(EC_TOPIC);
  mqttClient.print(ec.mS);
  mqttClient.endMessage();

  // post pH to MQTT server
  mqttClient.beginMessage(PH_TOPIC);
  mqttClient.print(ph.pH);
  mqttClient.endMessage();

  // ensure sensors are not probed too frequently
  delay(1000);

}

Once you get all the materials you should first assemble the components. Connect the pH and EC board together using the Qwiic-to-Qwiic connector, then use the Qwiic-to-male connector to hook up one of these boards to the Arduino (doesn’t matter which one). Connect the black cable to ground, red cable to 5V, blue cable to SDA, and yellow cable to SCL. Set up your board according to the instructions in the Arduino MKR wifi 1010 getting started page, modify the code above to properly include information about your wifi network, calibration solutions, and MQTT server, then upload the code. The Arduino will connect to your Wifi and MQTT servers and automatically reconnect when there are connection issues.

The above code will also post the readings of the pH and EC sensors to topics PH1 and EC1 respectively if you add an input in MyCodo to capture these readings you should be able to store them and take control actions using the MyCodo interface. Additionally, the Arduino code will respond to calibration requests published to the topic “CALIB1”. For example, if you want to calibrate your EC sensor with a two-point calibration method with a standard solution with an EC of 10mS/cm, you would put the electrode in the calibration solution, then send the message “EC1_HIGH” to the CALIB1 topic and the Arduino will perform the task as requested. The code assumes you will want to do 2 point calibrations for both EC and pH, with the calibration events triggered by EC1_HIGH, EC1_LOW, PH1_HIGH, and PH1_LOW. Note that the definition of the EC and pH values of the calibration solutions should be changed to the solutions you will be using within the code. The high/low values in the code, as is, are 10mS/cm|1mS/cm for EC and 7|4 for pH.

In hydroponic growing, we are often faced with the need to adjust the nutrient concentrations of a fertilizer reservoir or foliar spray directly, in order to increase the quantity of some nutrient by a specific amount. Although you can use a program like HydroBuddy in order to quickly calculate these values, it is often the case that these calculations need to be done in the field or in a growing environment, and a computer to calculate things is not at hand. For this reason, I have created a small “cheat sheet” that you can use in order to figure out the amounts of salts that you would need to add to a solution to increase any of the macronutrients by 10 ppm.

With the above cheatsheet, you can quickly evaluate some of the most common options you would have to increase all the different macronutrients in a hydroponic or foliar solution by 10 ppm and which secondary elemental contributions you would get from these additions. For example, if you add 0.0694g/L of Calcium Nitrate, this would add 10ppm of Nitrogen as nitrate plus 13.19ppm of Calcium. Careful consideration of secondary contributions need to be taken into account, especially when using salts that contain elements that can be toxic, such as chlorides.

Please follow this link, for an updated an easier process for the synthesis of mono/ortho-silicic acid.

During the past several years, there have been a lot of “mono-silicic acid” products being marketed for their use in hydroponic culture. These differ from the traditional potassium silicate based products in that they are very acidic in their concentrated form and are stable in solution for longer periods of time at the pH values used in hydroponics. While a hydroponic nutrient solution that has potassium silicate added to it and the pH adjusted to 5.5-6.5 will generally see extensive polymerization of the silicon-containing molecules within 24 hours, these stabilized mono-silicic acid products will be stable for far longer periods of time. They are therefore ideal for use in recirculating systems, where potassium silicate additions can be less effective.

If you watched my youtube video on silicon in hydroponics, you’ll know that the most common way to produce these stabilized products is quite complicated and involves the use of silicon chloride and very specific reaction conditions. These are unavailable to hydroponic growers, reason why it is not easy to produce a home-made version of choline stabilized ortho-silicic acid (ch-OSA). However, choline is not the only reagent that can be used to stabilize silicic acid in solution, and research in industry has shown us that it is actually possible to form stabilized silicic acid products starting from potassium silicate itself.

This patent describes how to prepare mono-silicic acid solutions that are stabilized by carnitine and several other additives, in the region from 0.01 to 8% silicic acid by weight. The great thing about this process is that we can start from potassium silicate, which is readily available. The concentration of Si obtained will be significantly lower than what is possible when generating ch-OSA – where solutions can reach 40% mono-silicic acid – but the fact that we can prepare it from readily available materials might compensate for this to some extent. It is also worth noting that this process comes from an unexpired patent, so it should not be used commercially without licensing the technology from the owner of the intellectual property.

Extrapolating from the contents of the patent and the examples given, we can come up with a process to brew our own mono-silicic acid at an 8% concentration. Here are the things you will need:

Note the amazon links below are affiliate links. This means that, if you choose to purchase through these links, I get a commission for your purchase, at no extra cost to you.

1. Potassium silicate (at least 32% K as K₂O)
2. Carnitine hydrochloride
3. Phosphoric acid (85%)
4. Propylene glycol
5. Distilled water
6. Scale to weight the materials (precision of at least +/- 0.1g, max at least 500g)

To prepare around 425g of stabilized mono-silicic acid, you could follow this process.

Before continuing please make sure you understand what you’re doing. Wear adequate eye and body protection, carry this out in a place with enough ventilation and make sure you read the material safety data sheet (MSDS) of all the materials used. These instructions are provided for educational purposes only, follow them at your own risk.

1. Add 10g of carnitine hydrochloride to a clean 1000mL beaker
2. Add 65g of distilled water to the mix.
3. Stir until all the carnitine hydrochloride dissolves
4. Add 10g of propylene glycol.
5. Add 240g of 85% phosphoric acid.
6. Put the mixture on an ice bath with ample ice.
7. Wait for 15 minutes, so that the mixture cools down.
8. During the course of an hour, slowly add 125g of potassium silicate to the mixture with constant stirring. Add more ice to the ice bath if needed to keep the solution cool. Note that predissolving the silicate in 150mL of distilled water and adding it as a liquid makes this process easier, although KOH additions might be required to complete its dissolution.

After this, you should be left with an acidic, completely translucid, carnitine and propylene glycol stabilized mono-silicic acid solution that should be around 7-8% w/w of Si as elemental Si. If there’s any precipitate in the solution then the stabilization process did not go well and the silicic acid formed polymerized into silica. This solution should then be used at around 1g/gal, which will provide ~18-20ppm of Si as elemental Si in your hydroponic solution. When using this solution,. the silicon present at the pH used in hydroponics should be much more stable than when derived from direct addition of potassium silicate.

If you go through the above process, leave a comment and let us know how it went.

The Hydrobuddy open source hydroponic nutrient calculator – which has been used extensively by both professional and amateur growers for the past 11 years – is finally making the leap to the Android platform. This is a big leap, as many growers – especially in developing countries – lack access to a PC but have easy access to Android phones. Thanks to the effort of the LAMW development team – who made the development of Android apps using Lazarus possible – I have been able to recode and port HydroBuddy to mobile and will release it for free and with NO ads within the next couple of weeks within the Google Playstore. The source code is already available on github and will be updated as the application development process continues.

The HydroBuddy Android application will include most of the features present in the desktop application. It will include all the same substances and formulations that are included in the desktop application and will allow you to perform the same types of calculations you do on the regular application. It is however true that some functionality will be missing initially. The “Copy Commercial Nutrient Formulation” section has not been implemented yet, neither have the “Water Quality Parameters”, EC estimations, or calculation of instrumental errors. The “Concentration from weights” and “set weight” calculations are also missing at this point in time.

Right now, the HydroBuddy application is in its internal testing stage, which means that only people who I add to the testing group are able to download and use the application. If you want to participate in this testing phase, you can download HydroBuddy in your Android device through this link. If you participate in this process, please share meaningful feedback about the application with me. This feedback can be left as a comment in this post as well.

The port to Android is expected to be a stepping stone towards HydroBuddy v2.0, which will include a complete recoding of several portions of the calculator. This will be done in order to implement a more flexible database structure that allows for more effective saving and sharing of the inputs and outputs of the program. The aim of this is to allow growers of all origins: hobbyists, industry professionals, or researchers, to exchange complete calculation sets and allow for a much more profound use of the calculator as a community-building tool.

Sadly there is no iOS version planned, since I do not own, or plan to own, any Apple devices, and therefore cannot program/compile/test code in this platform. However, the licensing terms of both the desktop and mobile versions of the application do allow anyone to port and publish the application in iOS, provided it is non-commercial and released for free, with no ads and under the same licensing terms (GPLv2).

As I’ve mentioned multiple times in my blog, moisture sensing is one of the most important measurements in a hydroponic crop that uses a significant amount of media. It allows you to properly time irrigations and avoid over or under watering your plants. Capacitive sensors are the lowest cost initial approach to adequate moisture monitoring of your media. In this post, we are going to learn how to use an Arduino with a gravity shield and a low-cost capacitive moisture sensor in order to accurately monitor the water saturation of our media.

An analogue capacitive moisture sensor like this one does not expose any metallic parts to the media and can be used for the monitoring of moisture content. This sensor is powered by 3.5-5V and gives you a voltage signal that is proportional to the dielectric constant of the media it is in. As the dielectric constant of media changes with the presence of water, so does the signal of the sensor. However, no specific voltage corresponds to a specific water content measurement by definition, so we need to calibrate the sensor in order to interpret the voltage values we read from it. In order to get readings from this sensor, I use an Arduino UNO, the above-linked capacitive sensor, and an LCD shield from dfrobot that I can use to easily get the device readings. The arduino code used for this device is also shared below.

#include <U8glib.h>

#define XCOL_SET 0
#define XCOL_SET_UNITS 50

U8GLIB_NHD_C12864 u8g(13, 11, 10, 9, 8); 
float capacitance;

void draw() {

  u8g.setFont(u8g_font_helvB10); 
  
  u8g.drawStr(0,21,"M_SENSOR:");
  u8g.setPrintPos(XCOL_SET,51);
  u8g.print(capacitance);
  u8g.drawStr( XCOL_SET_UNITS,51,"mV" );
  
}

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(4, OUTPUT);
  Serial.begin(115200);
  analogReference(DEFAULT); 
  Serial.println("MOISTURE");

  u8g.setContrast(0);
  u8g.setRot180();
}

void loop() {

  draw();
  capacitance = analogRead(1);
  Serial.println(capacitance);

  u8g.firstPage();
    do  {
      draw();
    } 
      while( u8g.nextPage() );   

  delay(1000);
  
}

The calibration of a moisture sensor usually requires the creation of what soil scientists call a “water retention” curve, which is a curve where you plot the sensor’s signal as a function of a fixed volume or weight of water added to the media. However, this approach involves the use of many different containers and the addition of water to the media followed by oven drying steps in order to accurately determine how much moisture was actually in the media for every measurement carried out.

In order to do this procedure in an easier manner, losing as little accuracy as possible, I have created a calibration procedure that makes use of natural drying and only requires one single oven drying step. The procedure is as follows:

1. Heat the media that will be used for an experiment in an oven at 110°C (this drives out all water).
2. Wait for the media to cool to room temperature.
3. Fill the container that will be used for the test (this can plastic but has to have holes at the bottom). Put the sensor in the media, make sure the sensor is driven into the media until the top line is reached.
4. Take a reading, this is the “completely dry” media reading.
5. Disconnect the sensor from the Arduino.
6. Weigh the container+media+sensor. This will be the “dry weight”.
7. Take the sensor out.
8. Add water to the media until there is ample runoff coming out of the bottom.
9. Wait until no more runoff comes off.
10. Put the sensor in the media, making sure you drive it in until the top line is reached. The sensor won’t be taken out for the remainder of the experiment.
11. Connect the sensor and take a reading. Take note of this value.
12. Disconnect the sensor.
13. Weigh the container+media+sensor. Take note of this value. The first reading you take is the “max saturation” weight.
14. Repeat steps 11 to 13 every 1-6 hours (time is not very important as long as you gather enough data points) until you reach close to the dry weight. This can take several days depending on the media used. The more points you measure, the more accurate your curve will be.

After carrying out this procedure, you can create a curve like the one shown below. You can use the difference between each weight and the dry weight divided by the difference between the weight at max saturation and the dry weight in order to calculate the water saturation percentage. As you can see, the curves for these sensors are fairly linear in the 40-100% moisture range for the media I tested, while below 40% the regime changes and the measurement increases exponentially until it reached the “dry weight” sensor value. The entire curve can be described with a power-law equation. This behavior will not be the same for all media tested, reason why it’s very important for you to calibrate the sensor for the specific media you want to use.

Once you have your sensor calibrated you can know what a measurement in mV implies in terms of water saturation for a given media type. This allows you to time your irrigations at a given water saturation % effectively. Which water saturation percentage might be better, depends on the properties of your media and how the water potential changes as a function of the water saturation. However, this allows you to experiment with irrigations at different water saturation % values and figure out exactly where you need to water so that your plants are not under or overwatered.

It is also worth noting that the above sensor is probably not rugged enough for use in a hydroponic setup without a bit more hardening. In order to use these sensors in practical applications, you should apply conformal coating to the electronics at the top of the sensor and then use shrink tubing in order to fully protect these electronics from the elements.