My tanks are consistently under 6.0ph. Not sure how low b/c my test kit doesn't go that low, but its low enough that I can't keep frogbit alive. I am considering adding some limestone rock from the local rock yard to bring the ph up. My tap water tests at 7.0-7.2 but after a week in the tanks it drops off the scale. Nothing in the tanks other than fish, gravel, water and using pothos for the nitrates. Can't keep snails alive and TSN are starting to get cloudy eyes. Thinking about adding a few rocks at a time to the filters, waiting a week or so, check ph and repeat if neccesary. Hoping to avoid the drastic ph swings during water changes and for better health of the fish. What do ya think???