Yellowish? sounds like nute stain, but why up at the basket?
This may be a silly question, is the roots getting plenty of bubbles up to the net?
Is there an odor of the roots? if not, and the roots aren't slimey, i think your fine.
It wouldn't hurt to treat the solution with 35% Hydrogen Peroxide (liquid oxygen), 1 tsp per gallon to kill off any bacteria.