I’m a cat lover and never had interest in fish keeping. My cat brought home a live but injured goldfish just over two years ago. I rescued it, but it can’t go back to a pond because of its injuries. (It lost a lot of gut through a hole in its belly, and now it excretes through the hole and doesn’t get bigger because it’s underfed, but I hate to kill it because otherwise it seems quite happy.)
I bought a second fish to keep it company and a 20 litre tank, on the advice of the local aquarium shop. I have gravel, no plants, a pump filter containing charcoal, and I replace the charcoal every month, the filter when it starts to break up. I rinse the filter in pond water every week to keep it clean, and I replace about 5 litres of the water.
Last summer someone else’s cat caught a third gold fish and I was black mailed into taking it – threat of it being eaten by the finder’s Koi Carp otherwise. Now I read that my tank is criminally too small for the poor fishes, but no one will re-home them for fear of infections.
Not only is the water filthy and brown despite repeated treatment with something from the fish store, but the fish are now lethargic, not feeding and two out of the three have big sores on their rear flanks in the same place. The biggest of the three doesn’t have any sores……. I think he is attacking the two smaller fish. I put medication in the tank, but to use the water cleaner and the medication the charcoal has to come out.
Is it okay to do a daily 20% water change? I don’t mind doing that since the fish go lively again when there’s fresh water, even though it stays brown. I use a water conditioner from the fish store, and never put in untreated tap water. I let it stand overnight to be the same temperature too.
I would like to rehome the two larger fish and keep the disabled one, maybe with a companion of a species that won’t grow big. I can’t euthanise her after two years, just because she’s making extra work for me, but clearly three fish, two of which have doubled their size in a year, to over three inches long, is far too much for a 20 litre tank.