Algae Growth on Rockwool Medium

by Phil
(San Diego, Ca)

How to cure algae growth on rockwool?

Answer: Phil- Unfortunately, prevention is the best answer for dealing with algae. Once you have algae, you constantly have small amounts of dying algae. When bits of algae die, microscopic fungi move in and begin to decompose them. The fungi attract fungus gnats, which will make a home in your roots and chew tiny holes in your roots. The tiny holes, of course, let in any pathogen that may be floating by in the water (there are ALWAYS a small amount of pathogens in the water normally).

These pathogens include pythium, wilt, and fusarium....any one of which could wipe out an entire garden pretty quick. In addition to all of this, the algae competes with the roots of your plants for nutrients!

Algae will grow anywhere it finds these three things- water, nutrients, and light. Since the whole hydroponic system is filled with constantly re-circulating nutrient solution, the only one of these three ingredients you are able to remove from the equation is light. Any place in the system where nutrient solution exists, you need to exclude light as much as possible. Keep your nutrient solution in a light-proof reservoir (with a lid). Make sure there is not light exposure where the nutrient solution enters the system and where it returns to the reservoir. For drip system, you can cover the tops of your planting medium with pieces of black plastic, with the drip emitters run underneath the plastic. Keeping the light off the rockwool will prevent algae growth on the rockwool.

Once you have algae in your system, you don't have very many options. Anything that kills the algae will almost certainly lead to fungus gnats. That said, you can still light-proof the system as much as possible. You can also add a small amount of Hydrogen Peroxide into the nutrient reservoir. Once you begin killing back the algae, you MAY want to change the nutrient solution more frequently (as it will become saturated with bits of dead algae). Be sure to read my page on using Hydrogen Peroxide if you decide to go this route, as the Peroxide can wipe out your entire garden just as quickly as pythium or fusarium if you use it improperly. I sure hope this helps you out Phil, and Happy Growing!