NFT issues...I`m clueless

Hi fellow growers,
After many succesfull Flood and Drain cycles I have decided to move forward into NFT hydroponics. Especially Growstream by GHE (terra aquatica). Unfortunately, here ends my enthusiasm.

I have encountered many issues. My first batch of clones died bc of stem rot, so I decided to ditch everything and start over with the same genetics, fresh clones.
To solve issue with stem rot I decided to get half of the clones out of the agrawool cube (plants close to holes where water spray out of the tube) and lower the water level inside the gullies just about half centimeter under the net cups.
That succesfully prevent the cubes to be constantly oversaturated, new roots are coming outside those net pots, BUT as far as they touch the water, they start to get brown and die.

And I wonder.... whats the problem?

Room temp: 28C day/ 24C night
Water temp: 22-23C all day
PH: 5,6
EC: 0,86
using H2O2 or purolyt doesnt make it any better

Pictures would help. Your ph is low for water growing. I wouldn't use drip irrigation right away I would let the plants grow and water by hand at first.

Brown roots could be overfeeding, dies in your nutrients, brown algae/root rot.

Try adding some bennies and mixing your feed strength at ⅔ strength.

Yeah...general rules.

I have already figured it out. Heavy metal poisoning... dont ask me how. Sometimes I look smart, but make dumb mistakes.

Source of poisoning is out and so are the roots out of net pots. In just 1 day majority of plants has roots growing into the water.

Case closed.