Since I added plants in my 45 gallon the ph keeps going down. I did a 50% water change today, came back 3 hours later and Ph is yellow, about 6.0. The water comes out of tap about 7.5 around here. My 5 gallon is also always acidic even after large water changes. I added some Ph buffer ever though I really didnt want to, but i'm gonna check again in a little while to see if the levels have gone up at all.