I read thru and from the first pics, (don't need so many), you got rot started.
Those organics AN talked a bout are just chelates and not like organic nutes so ignore that.
How strong is the peroxide you used? I've used 4ml/L daily for 4 days then every 2nd day for a few more treatments of 35% food grade to successfully fix that exact problem. Chiller prevents it from even starting and never had to use peroxide at all after building one and keeping the nutes at 65 - 68F in Rubbermaid tubs.
Health food stores and most hydro shops will carry it.
Do it quick.