There are many brands of hydroponic nutrients.
I use GH, so again, these are the products I will use to explain how they work and what they do.
Hydroponic nutrients usually come in either liquid or powder form.
There are organic nutrients and nutrients made from mineral salts.
The main 3 that are called Macro Nutrients and are usually in every fertilizer or nutrient to some degree are NPK.
Nitrogen, Phosphorus and Potassium.
These are used in the largest quantities.
The numbers that you will see on any fertilizer are in the order of Nitrogen Phosphorus and Potassium.
You can expect dry, or powdered fertilizers to be very close to the numbers on the package as they are mostly closely regulated.
Liquid fertilizers can vary wildly, and some have been known to often not have what is advertised at all in the bottle.
I stick to ones that I know, as do most growers. More expensive doesn’t always mean a better product.
In a complete hydroponic food, you should also have Secondary nutrients which are Calcium, Magnesium and Sulfur.
Also, there are micro nutrients which are very important in a hydroponic solution.
Theses are Iron, Copper, Zinc, Manganese, Boron, Molybdenum and Chlorine.
A great additive or element that is commonly used in hydroponics is Silica.
This strengthens stems and leaves. A very important component if you are growing a plant with large weight in flowers.
This strength also helps with pest management as most pests that eat plant material do much more damage to soft, easy to chew plants.
I’ve made my own plant food by following recipes and tweaking them for my own use, but it really isn’t worth the bother when you have companies that devote millions of dollars trying to figure out how to make the perfect food for your hydroponic solution.
We already talked about the 3 main stages of growth.
Rooting or seedling, vegetative and flowering.
During the rooting, seedling and flowering stages, plants can use more Phosphorus than Nitrogen.
During the vegetative stage they thrive with a higher nitrogen solution.
When you see the first number (N) is higher than the rest, that means it is mainly used for vegetative the stage or plants that you don’t even want to flower like lettuce for instance.
When the second number is higher (P) then you know that this is used for the flowering stage.
There is a lot more science to nutrients and fertilizers than this, but again, there is much more than the scope of out time here will allow.
If you want to know more there is a good article on nutrients and additives in the Garden Culture How its Made issue.