Yep I see this question come up a LOT on this forum and it's almost always that. People switch to strictly bloom food and stop giving the veg food so the plant takes nitrogen from the lower leaves and they go yellow. This is normal to a point (just like how tree leaves turn yellow in the fall) but do give them a little veg food and maybe cut back a hair on the bloom so you don't over nute them. =)your obviously using bloom foods
they want N, give em a dose of veg food
Hey Serapis....See my advise on your other thread about these very same plants... ;p