Substrates are an essential part of many hydroponics systems. They provide support for the plants, replacing soil in this respect, though hydroponic substrate media must always be neutral and never change the pH of the water or add any nutrients to the system. Common substrates include rock wool, coconut coir, clay pellets, sand and pea gravel. In many cases, you can use the substrate for multiple plantings, but to prevent transmission of disease it must be sterilized after every harvest.
Remove all plants from the substrate, and remove the substrate from the system.
Dump the substrate media out of the pots and into a bucket or other container large enough to allow you to cover it completely with liquid.
Mix 4 teaspoons of bleach into each gallon of water, and pour it carefully over the substrate. Allow it to sit at least half an hour, stirring gently if necessary to ensure all the substrate comes in contact with the solution.
Drain off the liquid and rinse well, rinsing repeatedly until you don’t get any more bleach smell from the substrate.
Take all of the pots from your hydroponic system once the plants have been harvested. Carry them to a safe area outside that cannot be accessed by children or pets. Leave the substrate in the pots but remove any remaining plant material.
Mix 9 parts water with 1 part bleach, and gently stir until it is completely mixed.
Pour the bleach solution over the pots until the substrate media is drenched. Stir the contents of the pots to make sure the bleach hits all parts of the media.
Wait for the bleach solution to drain out of the pots.
Rinse the substrate well, stirring if necessary. Once all of the bleach is gone, the pots and substrate can be reused.