If you used the same water in both systems, the water wasnt the root cause. I use reverse osmosis for aero because it provides tighter control over the nutes, the only stuff in it is what i put in it ;)

My thoughts exactly but I'm 100% sure every water change (without anything else added) caused root rot the following day.

Not an answer to your question but you might want to look into earthworm castings/compost tea. It cured my root rot and other rhizome problems.

I wouldnt recommend running organics with aero unless its low pressure or AA.

Edit: didn't read question properly. Not sure how well ewc tea applies to aeroponics. I don't know enough about aeroponics to say.

Well sadly the RO filter didn't fix my problem. Roots on the left are 12 hours into the freshly filtered tap water.

The system itself is infected, disinfect everything very thoroughly including the pump, replace any tubing, netpots and neoprene collars.

@Gardev

Organics tend to block nozzles and pipework. Low pressure and AA aero use larger orifice nozzles which can tolerate solid particles better. This includes biofilm that is naturally slewed as new replaces old.

It's probably not your water.root rot is just what happens when roots die,they usually die in hydro from lack of oxygen,maybe this site will help ya out http://growww.weebly.com/hydroponics.html

It's definitely the water. I moved a healthy hydro plant to a cup of tap water and it rotted in 12 hours. Oddly enough leaving the plant in the same glass of tap water that rotted it allowed it to grow white roots after 5 days.

So you still haven't figured it out? I'm just curious

Getting closer. I reran a couple tests and RO+DI filter seemed to leave my roots perfect. Just using the RO filter seems to have worked the 2nd time with a just a little browning but that could be in my head. I just changed my water in both systems today with RO+DI filtered tap water. I'll see how that works out

Did ro system kill the pythium?