Hydroponics gives the grower a lot of control over their plants compared to soil growing, but it also presents its own unique challenge. Perhaps the greatest one is having to manually add nutrients. Plants usually get their nutrients from the soil they grow in, but when there is no soil then they need to get their nutrients elsewhere. This is where liquid nutrients come in.
Hydroponic nutrients are different from regular fertilizers because they are acting as a soil replacement, as opposed to a supplement. Most hydroponic nutrients contain all these elements: Nitrogen, Potassium, Phosphorous, Calcium, Magnesium, Sulphur, Iron, Manganese, Copper, Zinc, Mloydenum, Boron, and Chlorine.
The temperature of the nutrient solution is also important to keep in mind. Ideally the solution should be around 70°F. Too much above or below that and your plants may struggle to grow properly.
If you want to learn more about hydroponic nutrients, check out homehydrosystems.com. They have all sorts of useful information about hydroponic nutrients.