Several problems here.
1) Do you use dechlorinator when you change the water? (No more than 1/4 of the water should be removed, or tank chemistry can be thrown off. AquaSafe is a good brand for this.
2)You need to change the filter cartridge once a month. Not rinse the sponge, which contains beneficial bacteria, but the blue cartridge needs to be changed, because the filter carbon it contains gets full and can no longer take carbon out of the tank, then you get nasty chemical spikes, which can very easily kill your fish.
3)Adding a PH buffer can help maintain balance in your tank as well. I personally use Tetra EasyBalance for my tank. This brand also adds nutrients to the tank as well to benefit fish and tank health.
4)be sure to vacuum your rocks. I usually do this at the time of water changes, since it takes out water anyways. Vacuuming the pebbles removes nitrates from leftover food and waste products.
Hope this helps
~Dormfish
1) The OP has already dealt with the question of dechlorination. There are times when a large water change is necessary, however I regularly change 50% of water with no ill effects. Many forum members recommend this amount as a weekly change amount, although my "standard" amount is 30%.
2) The carbon filter does not need to be in there at all. It is only really useful for removing medication from water. Once it has been in there a while, the carbon is useless, but it does become a home for bacteria. Then you change it, and throw away the bacteria. You do need to rinse the sponge, in old tank water, to remove the gunk, you will not wash away any bacteria by doing so.
3) I don't want to comment on this suggestion.
4) At last, we agree!
