Yellowing Leaves

Okay so here's a little background... I grew a crop of commercial seeds and everything came out good, got some medical seeds and started these, the guy at the local garden store has me test my water and the pH is too high. Bought the pH down, and have been using that faithfully on these ladies and we are around week 5-6 now and they are yellowing. They are fed once a week like the first crop, anyone know whats going on?<br />