Slime,algae,bacteria?

I agree with steve. Light leaks, keep the water temp in range, and clean everything. Clean your airstones with h2o2 every reservoir change. Wipe the sides, the lid, the air stone lines with h2o2. I always had better success with beneficial root bacteria, but you don't need anything if you have your environment dialed in. I will never be convinced root trimming is a good idea in a cannabis homegrow (until I see some actual scientific white papers/research done), unless you have to cut out root rot. It slows the plant down, reduces its' uptake of nutrients and doesn't improve the overall root mass. There are white papers stating this, while there is 0 proof proving root pruning is beneficial in a cannabis homegrow. You don't have enough air, so trim roots? doesn't make sense... your plant is 6 inches tall.. if that were the case good luck in flower.

* you don't need "root cultures" with 100% suluble and plant ready nutrients -- which all "hydro" nutes are, if they aren't trash. h2o2 is not going to harm your roots. it's commonly used in nurseries and gardens all across the world with no problem. is it needed? maybe, not.. but not for that reason. if you have brown slimy stuff on roots (brown on its own is more likely staining that you can ignore) then h2o2 is an excellent option to control or fight back whatever is growing on your roots... never be afraid to use h2o2, but do have a good reason. there's such a thing as 'too sanitary' . .. having some 'good' microbes helps reduce infection of bad microbes through competition of resources... you can go 1 of 2 ways.. using this sort of mechanism to maintain the system (in this case h2o2 is bad idea) or you use things like h2o2 to keep it sanitized. which is better? no idea... haven't read any research on it and what ppl observe in their volatilr environments whle engaging in a hobby is not 'research'

light leaks? this is usually hte primary problem. Or, too warm? you'll have to scrub the reservoir on occasion if it's a common issue - pre-empt the issues based on how long it takes to form. i don't use anything in my rez. it's drawn down about 85% every 4-5 days and refilled. no h2o2 no rmicrobes. i keep it dark and fairly cool (<70F.. prolly 66-68F?). I don't scrub or clean it during a run. Darkness and cool temps are the key. Even so you may need some sort of regular maintenance. Go on smell too.. water shouldnt' smell bad, lol. If the reservoir is large, use agitation over bubbles to aerate and avoid stagnation. a vortex will be significantly more effective at adding o2 to a reservoier than air bubbles. incontravertibly true if you understand how gasses dissolve almost immediately to reach equilibrium and how water flows within itself... churning is WAY better at oxygenating than bubbles drifting to surface. And, it'll prevent microbial growth to some extent with constant motion. Much harder for stuff to latch on to sides to form a colony etc...

Okay so I been in your shoes when I started Hydro. The best solution I found is you need to prune your roots as they grow, and develop. Plus stop using h2o2 it does more harm then good. Your roots are rotting due to not enough air. It will likely mess with your whole grow from here on. If you stop the rot from starting it won't cause you a issue. Then you can have healthy root cultures to naturally protect the roots vs chemicals that kill those cultures. I know how you feel.