red composting worms are water tolerant. you can toss some in your grow basket. they thrive in hydroton as long as there is moisture. not sure about rockwool. they will eat dead roots, fungus, insect eggs/larvae, basically anything/everything.
if you're not so adventurous, have you tried an endomyco product? great white? that stuff colonizes the root cortex itself, fights infection from the inside out. enzymes might also help break down proteins and dead organic matter. i'm under the distinct impression that enzymes don't kill bennies. those enzymes are actually what some strains of beneficials produce, if my understanding is correct. all that costs $$$ though.
H2O2 will definitely oxidize and kill the bennies. it will probably denature the enzymes as well and render them non-functional.
also, low DO might also be an issue. how well is the entire system aerated? does the solution get constantly circulated? res volume?
was light hitting the roots?
what pH and ppm/EC were you running?
algae and pythium prefer higher pH (7.0+). keep it on the low side (less than 6.0). that will also keep your nutes in solution instead of caking on your equipment and roots.
as far as ppm, there is absolutely no reason to use high ppm if your plants aren't sucking down like 500 ppm per day. 1200ppm isn't going to feed your plants any faster. let's say your plants are absorbing 300ppm over the course of a week from your solution. what's the difference between 1200-900ppm and 600-300ppm? 600-300ppm is actually going to absorb faster due to a better osmolar gradient.
after a few days, if you're topping off your water level with plain water (RO or tap), you should see ppms go down. by the time you flush, your ppms should be much lower, say 300ppm or less. if you started at 1200ppm and you're still at 1000ppm when you flush, you've basically just wasted 1000ppm worth of nutes. you could've just mixed to 500ppm and gotten the same (actually, slightly better) results.
the reason i bring up ppm (or EC) is because those nutes can feed algae, especially nitrogen.
and if you don't want to EVER have to worry about this kind of stuff again, i mean 100% sure it ain't gonna happen, then look into aquaponics. i had several experiences exactly like yours, found aquaponics, and will never go back to plain hydro. it just seems so silly to do things that way when there is clearly a solution to make these problems go away permanently. you get all the performance of hydro without all the bullshit.
