My son has a small aquarium, and the goldfish in it has suddenly taken a turn for the worse. The fish has been languishing on the bottom for a couple of days now; still breathing (gills flap), mouth moving, but he basically just lies there or occasionally moves to a new location. His fins and tail look like they’ve been chewed up, but the only other fish now in the tank is a small tetra.
Any guess what’s wrong? I figure he’s a goner, but am curious so that I avoid the problem with future fish.
When was the last time you changed the water? And do you have a pH kit? you could the water to see if it’s too acidic or basic.
Also, when were the tetra and the gold fish put together? Whenever I add a new fish to a tank, or change the water, I put a few drops of stress coat (which you can find at any pet store or department store that sells aquarium items) in the tank. That returns a protective, slimy coat to their scales and fins, that may be compromised with the addition of a room mate or new water.
Also, does his breathing/gill-flapping appear to be strenuous, or just normal? Rapid? How is the tetra’s breathing and fins?
They also make dechlorinator. Sometimes new water can be sorta harsh.
How cold is the water? Should be above 72°F as I recall.
Aquarium may be too small. Then no2 .the most common problem is overfeeding.
The “chewed up” fins sounds like either fin rot (a fungus) or chemical burn (Ammonia or Nitrite). The first step would be a 50% water change, and as suggested by Shark, try adding some stress coat. Also, please check your water parameters. If you do not have a test kit, your local pet store should test for free.
You might have a problem with your filter. If water flow is reduced to a trickle, the bacteria in the filter may die off, allowing ammonia and/or nitrite to build up. Also, less water flow leads to lower levels of dissolved oxygen in the water.
Is the fish still interested in food? If not, this suggests a serious problem.
How big is the fish, and how big is the tank? You mentioned there is only one other fish (a tetra) in the tank. Please note, both these fish are social fish, and do best in tanks with others of their kind. If this is a small tank, you may not have room for additional fish. Overcrowding can cause some fish to become aggressive. Tetras are not known as “fin nippers,” but this behavior is possible if the conditions are crowded.
Consider a larger tank. Bigger tanks are also easier to maintain, because fluctuations in water quality will not be as severe. Do not add any fish to this tank, regardless of size, until the symptoms clear up.