This tank is 55 gallon and is very well established. It has held other fish for about 6 months before I got these fish. There are 9 fish in the tank, all about 1 1/2 inches to 2 inches long. Like i said, I have been having some weird test results using my current test kit and I am currently looking around for a test kit that I can also test for water hardness and all that.
The reason that I do my water changes the way I do is because I have been having some problems with 'sludge' in the filter. I dont know how else to explain it, but it is something that happens during summer. The sludge is almost like a whole bunch of flake food get wet and is clogging things up, but until a week ago, I hardly ever used any flake food as the previous occupants were eating frozen food almost exclusively.
I bought this tank as one of those 'kits' from Walmart and so the filter is basically nothing special, however, I have also added an aquaclear 200 filter and so I should be filtering something in the range of 400 gallons of water an hour.
So, basically I am forced to rinse the filter media about once a week, which I do in the water I take from the tank. I was advised to do this from another thread in this forum and to limit the amount of water I take from the tank so that I am not completely depleating the bacteria levels.
If this is way off base, let me know so that I can change my methods. I am still very much learning about this hobby and how to keep things going well. Like I said before though, it is not really like an itching epidemic or anything and is really limited to about two fish in the tank right now. I will go out and get me a better test kit today and I will let you know if anything is different.