the leaves seem to yellow faster when plants are in containers. and what exactly is wrong with pond water? fish and other animals live there, mammals most likely drink from it. its fine. the only nastyness in any natural watersource, is the crap ppl dump in there. anyway ur transitioning into flower now, and more and more leaves will yellow faster, im also doing a container grow and lower leaves have started yellowing quite a bit faster now that flowering has begun, just up the amount ur feeding them and they should be good. idk why ppl think tap water is so much safer than pond water, imo theres unknowns in both and unless u want to send both to a lab, to see whats all in it, we wont know. just becuase ur tap is clear and smells nice, doesnt make it better