I have a 20 gallon hexagon with a few Angelfish in it. I have had the tank set up since last June and the fish are doing fine. I have been having a few problems with the water tho. For some reason it won't hold the PH or alkalinity. I have been told something in the tank it causing it to loose its buffering ability. Right now my alkalinity is as low as it can go and my PH is at 6.0 I let the water from my tap sit out all night and while the PH is still very low the alkalinity in the water is right where it should be. So the PH is easy enough to fix but once I fix it and put it in the tank with in 2 days it is back down to 6.0 maybe even a tad lower. Here is a list of things that I have in my tank. Heater(marineland), airstone, fake plants (fairly new) and gravel. OHH I just thought of another issue. When I change the water(not even half) a few hours later the tank becomes VERY cloudy and will stay that way for several days. So a few days ago when I changed the water I made a point of not cleaning the rocks. I was thinking that maybe last time I took out way to much good bacteria. Well low and behold it got all cloudy again on me. I am really at my wits end. The guy from the local aquarium pet shop said to bring in my water from tap and tank and he will test them for me. Does anyone have ANY advice for me. Thanks.