Even though there has been great effort by many people to show hydroponic growing as something that can be done by anyone with little knowledge, it has come to my attention that many novice and commercial gardeners fail because of their inability to properly interpret the chemical phenomena around them. One of the variables that is primordial in hydroponic culture and that is grossly oversimplified in most literature about hydroponic gardening is the treatment of pH. For this reason, I decided to create this pH FAQ post in order to answer (in a basic but scientific way) the questions most people have (or should have anyway) about the science of hydroponics.

How can I correct pH changes ?

Bases or acids can be added to hydroponic solutions in order to increase or decrease the pH value of a solution. Bases and acids should be added as solutions and the amount added must be recorded in order to know how nutrients are changed. For example, if a potassium hydroxide solution is added to increase the pH of a solution, the amount of solution added needs to be recorded in order to know how much potassium was added to the solution (since this is a nutrient). Common acids to lower nutrient solution pH values are nitric acid, phosphoric acid and citric acid. I would recommend the use of citric acid to reduce pH and potassium carbonate to increase pH.

What is the ideal pH value ?

It depends on the specific plant you are cultivating. Most crops grow very well with pH values between 5.5 and 6.0, although there are some plants which require more basic or slightly more acid pH values.

How can I stop pH from changing ?

Please refer to the article I wrote about controlling the pH of your nutrient solution with buffers in order to effectively prevent pH variations inside your hydroponic nutrient solution.
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When researchers first started to study how plants grow and what plants exactly need to develop, they found out that plant needs are very different from our own. We, as humans, need minerals, vitamins, carbohydrates, proteins and fats amongst other substances. However, plants seemed to require a small assortment of inorganic substances from which they synthesized a very large variety of organic materials.

Many hydroponic growers are confused by the fact that nutrient needs and nutrient solution compositions are provided in the form of elemental concentration. That is, hydroponic solutions are often described in the form “N 200 ppm”, “K 100 ppm”, etc. Compositions are expressed as the amount of milligrams present of a given element per liter of solution. Nonetheless, this does not mean that the element is present as a pure substance.

For example, the fact that a hydroponic solution contains 100 ppm of Nitrogen, does not mean that the solution contains nitrogen as elemental nitrogen, that is, N2 gas. This in fact, does not express the form in which nitrogen is present, it may be present either in the form of NO3(-), NH4(+) or other molecules. This has caused some confusion since some people are unaware that hydroponic nutrients are mainly inorganic salts that, when dissolved in water, form ionic substances which are the actual nutrient assimilated by the plant.

It is important then to have a clear mental perspective about the way in which things are expressed and the way in which they really are. For example, you can have a hydroponic solution with 100 ppm of P. That is, a hundred milligrams of phosphorous present per liter of solution but in no way does this express the way in which phosphorous is present within the solution. Phosphorous may actually be located as a large assortment of ions, either H2PO4(-), HPO4(2-) or PO4(3-).

The reason why nutrient solution concentrations are often expressed as mere element concentrations instead of actual available form concentrations is because it is much simpler to think about the sum of all the available forms of a nutrient than each nutrient form by itself. In the light of the previous example, it is much easier to say 100 ppm of P than to state a specific concentration of each ion, given that (in this case) all ions are indistinguishable for the plant.

The really important thing about this is that the grower should have a clear understanding of the nature of hydroponic nutrients. Nutrients are really ions, which are formed by the dissolution of salts in water. So when you go out to buy nutrients for your hydroponic solution you should look out for inorganic salts of the desired elements ! (below, an image that graphically shows ion dissolution)
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A nightmare for many growers inside the hydroponic industry is the fact that pH adjustments need to be made every now and then to nutrient solutions. In fact, people often adjust the pH of their nutrient solutions several times a week in an effort to keep the values close to those considered ideal. However, most growers are unaware of the basic facts surrounding pH changes and how they can be avoided (please refer to the pH FAQ for more information).

The concentration of H3O(+) ions, which are the ions that determinate pH, changes according to other ions present inside the hydroponic solutions. Since plants take ions (which are charged species), outside of the solution, they cause a charge imbalance which is compensated by the generation of either H3O(+) (if the plant absorbs an ion with positive charge) or an OH(-) (if the plant absorbs an ion with negative charge).

One of the ways in which this pH change can be effectively controlled is by the addition of a specie which balances out this charge and offers reactivity against either OH(-) or H3O(+) species. Such addition of species to a solution in order to offer a chemical equilibrium protection against pH changes is called “buffering”. In hydroponics, solutions are most often “buffered” using ammonia, however, we can carry out simulations to see how this two ions act against “acid” or “base” additions and see how the entire hydroponic system reacts to this.

The simulations are carried out using the Maxima software and all the equation systems are generated according to equilibrium equations, mass balance equations and charge balance equations (this is called systematic study of the chemical equilibrium). Concentrations for all the buffering agents were treated as 0.1 mM.

Long story short, the graph below shows the results for my simulations of “acid” or “base” additions using three different buffer agents. The blue line shows the change when citric acid/citrate is used as a buffering agent, the orange line shows when ammonia is used as a buffering agent and the yellow line shows when carbonate/citric acid is used as a buffering agent.
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As it can be seen, citrate provides very good buffering capacity towards acid pH values while it’s buffering potential towards basic pH values becomes lesser. Ammonia provides almost no buffering potential towards acid pH values while it provides almost the same buffering effect towards basic pH values than citric acid. Note that basic pH buffering seems the same for both buffers because here the effect of the phosphate ions inside the solution becomes more prominent.
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However, when carbonate/citrtic acid is used as a buffering agent, it suddenly turns the solution’s buffering power towards both acid and basic pH values, extremely high. That said, it should be expected for a solution with this buffering mix to last several times more than a regular solution without needing any pH adjustments. In practice, the preparation of this solution has given me at least three weeks of plant intake without any need for pH adjustment.

In today’s world, things seem to have started to shift towards a more “natural” look at things. People are starting to reject synthetic and “artificial” things in favor of the more “natural” and “earthy”. Well, as a scientist, I have to say that most people have some very bad misconceptions about these definitions and their “evilness” or “goodness”. Let us start from the beginning.

What is Natural ?

This is usually defined as something that comes from nature without any fundamental modification caused by humans. Therefore, you could say that blood is natural, algae oil is natural, bones are natural, etc.

What is Unnatural ?

Something unnatural can be defined as not coming or not belonging in nature. You could then say that a bee swimming is unnatural or that a plant growing inside a PVC pipe is unnatural.

What is synthetic ?

Something synthetic can be defined as chemically manufactured by humans from chemically different materials. For example, plastics are synthetic, pure sodium is synthetic, carbon nano tubes are synthetic, etc. Now see that this definition is not exclusive, something can be synthetic but present in nature, like synthetic hormones, synthetic vitamins, etc.

Now which is bad and which is good ?

This is where most people have it wrong. Natural things are good ? Well, that depends, which natural thing. You eat and orange and it’s good, you swallow a scorpion and its bad. Both things are natural. Nature produces things that are toxic and lethal, but nature also produces things that are good for you. You cannot judge something to be good just because it belong inside a group, every category has both good and bad things.

Are unnatural things bad ? That depends. You smell a neurotoxin, you are dead, you use a sulfonamide antibiotic when you have an infection and your cured. It all depends on the specific thing your talking about and the specific use your giving it. There is no sense in judging something as being good or bad for the sake of it.

Now, are hydroponic nutrients unnatural ?

No ! Hydroponic nutrients have the exact same chemical form nutrients have in soil. Plants cannot absorb these nutrients if they don’t have these specific forms so hydroponic nutrients are indeed natural. They are the exact same molecules that are found in soil. Hydroponic gardening is just a form of manipulation in which plants are given an amount of these nutrients that fits their needs optimally. It differs from their natural conditions in that hydroponic growth conditions are better. The plant gets all it’s nutrients in the same form it gets them from the soil without needing to break up organic matter to get them or fighting pathological microorganisms. Indeed, hydroponic gardening has both positive and negative qualities, just like everything else !

This hydroponic nutrient solution was developed by Hoagland and Snyder in 1933 and it’s one of the most popular solution compositions for growing plants (in the scientific world at least !). The Hoagland solution provides every nutrient necessary for plant growth being appropriate for the growth of a large variety of plant species. The solution described by Hoagland in 1933 has been modified several times (mainly to add iron chelates and the like, but you can use the salts you normally use for preparing your solutions as long as you append to the concentrations given for each element) but the original concentrations for each element are shown below.

N 210 ppm
K 235 ppm
Ca 200 ppm
P 31 ppm
S 64 ppm
Mg 48 ppm
B 0.5 ppm
Fe 1 to 5 ppm
Mn 0.5 ppm
Zn 0.05 ppm
Cu 0.02 ppm
Mo 0.01 ppm

As you may notice, the Hoaglands solution has a lot of N and K so it is very well suited for the development of large plants like Tomato and Bell Pepper. However, the solution is very good for the growth of plants with lower nutrient demands such as lettuce and aquatic plants with the further dilution of the preparation to 1/4 or 1/5.

Also remember that the amount of iron you use should be in proportion with the amount of phosphate placed inside the solution, when used at higher strength, there exists the possibility of iron precipitation if non adequate chelates are used. If possible, try using DPTA instead of EDTA (which is not so good a chelating agent for hydroponics).

Hydroponic gardening is a great way in which plants can be grown and cultivated with yields far superior to those of traditional soil based culture. However, the last frontier of hydroponics remains being indoor growing. Light, which we take for granted because of the sun, is a crucial factor for plant growth and becomes dramatically diminished or non existent inside our house’s or building’s interiors.

The solution, of course, is using artificial lighting to grow our crops. Unfortunately, the amount of light needed by plants (which is measured in Lumens) is quiet high. In order to fulfill a plant’s light needs, high power consuming artificial lights must be used. In fact, most indoor growers use halide lamps which are in the range of 1000 to 2000 watts of power.

The amount of energy consumed by these growing lights is so huge because most of the energy provided to the lights is wasted as heat and little of this energy becomes usable to the plant as light. Other problems also arise because of the excess heat eliminated by this high-powered illumination devices.

The solution for this problem is actually very simple. The use of LEDs (light emitting diodes) for hydroponic growth has become popular because of their low energy consumption (almost 20 times less than regular growing lights). They are simple to install and provide all the necessary wavelengths your plants need for adequate growth. For instance, two tomato plants can be grown with as little as 50 W of growing LEDs while this same tomatoes would consume in excess of 1200 W with traditional lighting. If you are wondering where these lights can be purchased, just search ebay for “growing LED’s” and a bunch of sellers that offer these products will come up.
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Lettuce is one of the most common vegetables produced in hydroponics. It is amongst the first 3 vegetables produced in hydroponic crops around the world with tomato and bell peppers. Most lettuce production systems are designed around two ideas, either the NFT (nutrient flow technique) system or the floating raft system. The later system is of particular interest because it is highly economical and can produce bast volumes of hydroponic lettuce.

One of the main problems with raft systems is that the fact that the nutrient solution is constantly stagnant demands the use of pumps to circulate water and generate significant aeration. Without this precious oxygen reaching the plant’s roots, floating raft systems experience high loses of yields in the form of dry weight, nutrients, etc.

Nonetheless, raft systems can be improved dramatically in order to avoid the recirculation of solution and aeration of the roots by mechanical means. This is done in an exceedingly simple way, by placing the raft not directly above the hydroponic solution but a few centimeters above from the solution itself.

The results are incredible. Without any mechanical aeration or movement, this hydroponic system achieves dry weights superior to any floating raft system published in peer reviewed literature. This research was done by horticulturist B. A. Kratky and was published in the year 2005.

So if you are searching for a cheap hydroponic system which can offer you lettuce in high yields with no power usage, this is precisely the way to go. I will publish a post soon showing how this can be done and how you too can enjoy this great system for lettuce cultivation.
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It has become a common practice for many hydroponic enthusiasts, hobbyists and even commercial growers to dispose of the nutrient solutions they have that “are not adequate anymore” by throwing them down the drain. Most of them are not aware than hydroponic solutions are environmentally contaminating.

Hydroponic solutions contain all the basic nutrients necessary for the development of photosynthetic organism. This of course, means that hydroponic solutions are the ideal source of nutrients for algae growth. When they are disposed of down the drain, the solutions cause algae blooms which are terrible for the environment because when algae populations dye massively, they deprive water of oxygen and cause the death of aquatic organism.

The solution ? It is actually very simple. Have a hydroponic growing container in which plants that you “don’t care for” are grown. For example, have a hydroponic growing container in which grass, weeds or other type of “low nutrient requirement” plants are grown. This way, when your hydroponic crop has a solution it can no longer use, pour that solution into your other hydroponic container. Now leave the solution for those plants to take care off for two months. Once this happens, the solution should be very depleted of nutrients and unable to cause any algae bloom of importance.

Even better, the “waste solution” container, can have plants you can use. For example, you can cultivate herbs with low nutrient requirements that are for indoor use and have them as the “byproducts” of your main hydroponic system. It is also excellent for growing grass for any cattle or horses you may have. (below a picture of papyrus, a plant that naturally deals with solutions with low nutrient concentrations)
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