I am using earth stone as the medium with
seeds started in rockwool cubes. The water is city water, my well is too irony for hydro I think. The PH of the water before anything added is around 7.0. CalMag I am using about 1/2 teaspoon per gallon. And Earth Juice as a PH increase and decrease. I have thought about it being a byproduct as well but not having much experience in hydro I second guess myself. I will send general hydroponics and email and ask. That is a good suggestion. The residue is slimy like algae but a brown color that flakes off very easily when touched. Smells like the
nutrients but that doesn't necessarily mean anything.
On a side note, I started my seeds in the rockwool in the net pots. I think I prematurely put them in the NFT system because their roots were not out the bottom of the pot yet. They look to be doing fine but I have a chance to clean it and not effect the plants that much if in fact it is algae. Thanks for the continued help!