Everything springs from the water in hydroponics. Within a system of gardening that uses no soil, plants may or may not be anchored by some other growing medium like a vermiculite-perlite mix or washed sand. Often plants don't even have that support and instead stay in place, for instance, within a hole cut into a raft that floats in the water. That water is referred to as "nutrient solution" since all the nourishment a plant receives comes from that liquid. The solution consists of a special fertilizer made just for hydroponics gardening. A plant is fertilized automatically as it drinks.
Add and mix the hydroponics fertilizer with the water according to the directions on the fertilizer package. Choose the fertilizer that is appropriate for the growth stage of your plant, mixing the amount of nutrient solution appropriate for your garden's needs.
Pour water into another container and allow that to stand until you need it later.
Let the nutrient solution mixture stand for a few hours or overnight.
Check the pH of the mixture.
Adjust the pH according to the needs of your plant.
Use the fresh nutrient solution in your reservoir.
Note the capacity of your reservoir.
Take a reading of the nutrient solution with the dissolved solids meter, also called an EC or PPM meter.
Write down the pH and EC or PPM readings of the nutrient solution along with the date. The EC/PPM tells you about the nutrient level in the water.
Take another reading of pH and EC/PPM when the water level has dropped, recording the readings and the date in your notebook.
Add water--not nutrient solution--to your reservoir until it is at capacity again, making note of how much water you added.
Test the nutrient level again. If it is at a substantially lower concentration than it should be, add nutrients a small bit at a time until the solution is appropriate.
Adjust the pH of the water if it has strayed far from where it should be.
Continue adding water to the reservoir as solution is used up. Recording your readings, adjusting the water as needed.
Drain the reservoir completely and completely refill with nutrient solution when the total amount of the replacement water you have added equals the capacity of your reservoir.
Switch from the growth to the flower/crop fertilizer just before flowering commences.