I have 2 tanks-20gal frag and 29biocube. I do the same in both,but my 29 ph is always low-7.7. I keep kh at 11 mag at 1450 cal at 450. I tried leaving refit um light on all day- did not work. I use acuavitro ph buffer daily. It will bring it up, then within a day drop back to 7.7. My other tank does not have this problem. Anyone have any ideas?