yes, this all can be VERY confusing. i was just as baffled as you when i started bro,
and every grower will have a diffrent opinion on h2o2/bleach, everybody has diffrent results with each. you want to do what works best for you/your system personally.
if you used organics nutes sometime in this grow, there is still organic residue in your tubing/pump etc..
you need to clean out the system and sterilize everything.
and befor you get ahead of yourself you should take a step back, and try to find what caused the problems in the first place. heat?light? stagnant water?
fix that first, this the key to the cure working(found personally the hard way, battled for 2 months with pythium, FINALLY got water chilled and havent had one problem since)
i would say since the h2o2 hasnt worked you should give bleach a try, its MUCH stronger then 3%.
i would pull plants from the system, bath roots, and sterilze the entire system, resivour,tubing,pump,EVERYTHING. wipe it all down with bleach water and rinse GOOD. mix a new soulution, return plants. and use a very small amount of bleach in the nute solution.
you need to get all the fungus,bacteria,worms, EVERYTHING out befor you see improvement.
ill keep checking back and help more with anything i didnt explain good =] lol