The tiny spots on the leaves look a lot like spider mites, but the yellowing leaves underneath looks like a slight nutrient deficiency. I don't grow in water, but it looks like it could be a few issues, although it is hard to diagnose without some more info and maybe more pics from further back that shows the whole plant in addition to closeups. I have had plants that mites loved, but others that were untouched that were growing along side the infested ones. I recommend checking your ppm/Ec if possible to get an idea of how much nutrients are floating around, as well as to check the Ph, as was recommended earlier. Out of kilter Ph ranges can cause deficiency symptoms as well, so the more info that is presented, the better the diagnosis is likely to be.
