Once you decide to grow a citrus tree the first step is to either find a suitable candidate from a nursery or grow your own from seed. If you want to grow from seed, beware that it will take the plant 3 to 5 years in order to start bearing fruit. If this is unacceptable, find a plant at a local nursery that has the age you require. If you are growing from seeds, soak the seeds inside a napkin for 2 days and then remove the external seed coating. This guarantees effective germination once the seed is planted.
For the best results, I recommend using a 5 gallon container filled with rice husk, perlite or vermiculite fitted with adequate tubing at the bottom for nutrient solution evacuation. I recommend installing a drip irrigation system with at least 3 drip emitters per citrus tree you planted.
As for the nutrient solution, I recommend using a Hoagland solution, first at half strength and then at full strength as the plant starts to grow. Your hydroponic citrus tree will not probably grow as big as an actual citrus tree but will bear fruit of normal size and sometimes even in the same quantities. Since your tree is in a hydroponics system, it will (if the solution is taken care of) never have to face any iron or manganese defficiencies common to soil grown citrus trees. Sometime in the next month I will publish a detailed how to on the construction of the hydroponic system itself.