Q. I have a 10-gallon tank equipped with a mini-power filter and an air-powered corner filter with a filter cartridge. The tank contains one swordtail, one glass catfish, one platy, one 3-inch chocolate cat, one 1-inch bumblebee cat, one upside down cat and a female betta. Do I have too many fish? How often should I change the water? Presently I'm changing one-third of the water twice a month. Is the filtration setup okay? I'm striving for the best filtration. Do either of the filters do any biological filtering?
A. I think you have a few too many fish in your tank for all of them to thrive and grow to become healthy adults. Your fish may appear to be doing well at the present time, but they are still small. As they grow and mature, they will need more space.
Your question about filters poses another problem. If you are cleaning your filters when you change your water, you are not allowing sufficient time for a biological system to develop. If you are unable to obtain a larger tank, consider switching the corner filter to a sponge filter, which will provide some biological filtering if you take care of the sponge when you change water. (By taking care of the sponge, I mean removing it to a bucket of the siphoned tank water, squeezing gently three or four times in this water and then returning the sponge to the tank when the water change is completed. Keep it wet and do not put it in chlorinated tap water or a sterilizing solution, which would kill the bacteria.)
Concerning your choice of fish, there is nothing wrong with the fish that you have in your aquarium (assuming we are both talking about the same species of chocolate catfish). They are all relatively peaceful and should not harm each other, but some of them are not being kept under their preferred living conditions. That is, the swordtail, platy and glass catfish are all schooling species that prefer to be with their own kind. These types of fish only show their best colors and normal behavior when similar animals are near. It's all right to have as few as three of each species, but much better to have five or more of any shoaling species when they are put into an aquarium. You will notice that they all swim near each other, even in a very large tank.