ph drop

Hey all, We're beginning to run into a new problem. Over the past several weeks our ph has been slowly dropping, to where now it's about 6.8. A few weeks ago it was holding steady at about 7.6-7.8. I know that our fish prefer the lower ph so it isn't an issue at the moment, but we don't know...

I have a 10 gallon tank that is cycled and has a couple of plants. I had three panda corydoras (starting to stock the tank, with the goal of 6 fish). Everything had been stable with weekly 25% water changes; the water parameters have remained 0/0/0. My region has hard water, and the pH has...