BRO! Brew some tea IMMEDIATELY! DO NOT ADD H2O2 or BLEACH (lol) to your rez. H2O2 will react with any organic matter. While this will kill any slime or sludge you have now the chemical reaction will destroy already week roots, cause them to die. Dead roots = more sludge, it will be a negative feedback look.
After reading through the thread I can tell your issues comes from two things:
1. NO PPM METER. You are giving plants nutes based on visual cues which is a NO NO for DWC. Hydro set ups are a Ferrari, and you are trying to drive one with unleaded gas. For hyrdo a real PPM meter and PH stick are a MUST.
When ppm is off the water becomes to salty for the roots. Plants absorb nutrients through osmosis and incorrect ph and ppm damages roots and they become necrotic, cause root rot.
2. Your net pots sat BELOW the water level for too long, causing root rot at the base of the plant.
THE FIX: IMO you need a pH stick, PPM meter, Great White, Hydrogard, Physan 20, bag of earth worm castings, molasses.
1) Flush your entire system with Physan 20. Wear gloves, it is very caustic!
2) During the Physan 20 flush brew some microbe tea (Great White, Hydro Gard, Castings, Molasses). Hieseberg has a great method.
3) Flush DWC, add 1/2 strength nutes USING UR PPM METER.
4) Pour Tea over roots according to Hiesenbergs Schedule.
5) Pray
The tea if done correctly will slowly kill the slime and you will recover, the grow will take much longer.
I saw a LOT of misinformation in this thread. There is no such thing as a sterile REZ. Commercial hydro growers do not add h2o2 to control contams, only to add Dissolved Oxygen to the water. If you do not have a DO meter you do not know if you need more DO or less. 1 air stone = plant should be plenty of oxygen.
Only grow with advanced nutriets, never organics.