In rockwool, you really need to feed them, there are ZERO nutes in there, nothing for them to feed off. Prob soak the rockwool for 10-15 minutes a day, only let the water reach about 1/2 up the cube, it will wick up the rest that it needs. I run 600w HPS in a flood & drain and basically the cubes take water 2x a day, but your LED has so little heat evaporation may not be as much. Do let the rockwool dry out some, dont want it drenched 24/7