The plant is on its third week, so wouldn't the hydroton be clean by now? i washed it all before I used it and I've been using it for 2+ weeks. I have one tub for mixing the nute solution, then I pour it into another tub which is the actual reservoir.

Right now in the rez are two airstones. the temp of res is about72f. the temp around the plants is about 78. Could it be the airstones?

My roots look OK i think. All of them are nice and white. reesrvoir is light-tight so i dont think its algae.