I have 66 gal freshwater tank. I have had it set up for about 2 months. I was able to maintain & breed mollies, until just recently. I noticed two of my older fish acting sluggish. I tested the water and found that the ph was zero & water was too hard. I added ph tabs as recommended through neighborhood aquarium store. That still did not fix the prob & I ended up losing all of my aquarium fish. Luckily, I kept the fries in a seperate tank. I feel that it's just going to be a matter of time before I lose them also. :?