04-15-2009, 11:33 AM
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In the past I have had fish that suddenly have difficulty swimming, just basically tumbling around, head down or head up when they do "swim" for a few seconds. I've never had such fish recover. I understand several things can cause this, from internal issues (swim bladder trouble), disease, sudden change in water parameters (temperature, pH). Others with more experience with this condition may have suggestions, but I would leave him alone, but recognize it probably will not survive; if it dies, remove it immediately.
A suggestion on water changes, you should do them weekly. It is more beneficial to the fish and the biological equilibrium to change less water more often than more water less often, as it keeps the tank more stabilized in terms of water quality. 25% is a good amount, but weekly would be much better, and I suspect your fish would thank you. Use a good conditioner with all water changes. Vacuum the substrate (gravel) with each waterchange but only skim the surface. Don't dig down into the gravel evey time, that can affect the nitrogen cycle too much. There's a lot of aerobic and anaerobic bacteria activity in the substrate and assuming it is in balance you want it to remain so.