I have a 55gal tank. I was having issues with pH being real low and my ammonia was real high. I read that if the pH was below a certain point and your ammonia was high then you had ammonium and that was not toxic to fish. I was finally able to get my ammonia to 0ppm and my pH was around 7-7.2. But I had to get new filtration cause what I had wasn't working. So I got Marineland penquin power filters. For the first week or so my ammonia was 0 and my pH was low. I thought it was from the water change. I put some pH Up in it and it brought it up to where I wanted it, around 7-7.2. But it didn't stay. It keeps dropping down to around 6.0 or lower. If I add pH up it goes up, but within 24 hours or less, it's down again. I just checked my parameters and my pH is 6.0 or lower, my nitrate and nitrite are within the safe range, but my pH is registering real high. My fish are fine. But I'm at wits in as to what to do to get the ammonia way down and get the pH up. Any suggestions or ideas are all welcome.