I have come to believe that its from the source, the water itself, and RO filters do not get algae out, h202 doesnt touch it, enzymes makes it explode, chlorine doesnt even touch it unless you want dose it at a leve that will toast your plants. washing the roots makes you feel better but it only hurts the plant IMO, Physan is an algaecide, it kills it
if you able to , take the plants out of the system and give it a serious cleaning, scrub it clean, if you cant take them out then
Physan is really your only option at this point. 1tsp per 15gals and let it run for 3 days, you should see a ton of brown bits on the wall in your control res. turn off your float valve and let the water level drop a couple inches, this should make most of the brown bits stick to the wall of your buckets above the water line that has dropped over the last 3 days, that way you can wipe them and get that dead algae out of the system, you will also have to spray the net pots because the brown bits get caught in the foam and stick to the lids of the buckets and top part of the net pots as the foam dies down
then you can refill the system, with the physan and a nute dose of about 500ppm, at this point your system should be clean and there shouldnt be many brown bits, if there are then drop the level again and wipe out, you probably dont have to drain the system from here (only if your still seeing a ton more brown bits then you will need to get that shit out of the system) , if everying is running clean then you should not do a change out for a little while, let the system run , dose you top up res with some physan as well, so that for the next 3 wks you know that all the water in the system is clean.
that should give you plants time to come back, one thing you wont see is over night changes to your plants, it will take a week or more. but the most important thing is to clean the system