My fish will only swim at the water surface

Question
Hi Chloe,
Thanks for the answer, but I don't think lack of oxygen is the problem. I have a 100 Litre Hexagonal tank, with 2 air stones. I have noticed today that my fish has some small red lesions around its mouth.
Thanks again.
Andrew
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The text above is a follow-up to ...

-----Question-----
Hi, I bought 2 Black Moor fish last Saturday. 1 of them is fine and looks really good and healthy. But my other 1 only swims at the surface of the water. It doesn't appear to be eating much food, and looks sad. It also seems to be bullied by my first fish. Any idea as to the problem. I checked the PH, ammonia etc of the water last week and that was fine. I was thinking of giving this fish a saltbath, would that help.
Thanks in advance
Andrew
-----Answer-----
Hi Andrew,
It sounds like there is a lack of oxygen in your tank. This can be cause by a tank that is too small. Keep in mind that a goldfish needs at least 10 gallons of water each. They also need a very efficient filteration system as they produce lots of waste. You could try a salt bath but consider the size of the tank to the fish you have. This could be your problem.

Hope this helps
Chloe.

Answer
Hi Andrew,
It sounds like it may be a disease called Enteric Redmouth. Little is known about it, and it is a relatively rare disease. It is an infectious bacterial illness, however, and therefore a good antibiotic such as Maracyn Plus should help treat it (or at least prevent it from spreading to other fish).

It definitely sounds like some sort of bacterial illness, if not Enteric Redmouth. Most bacterial diseases in fish are extremely dangerous, and they can wipe out entire tanks of fish in a matter of days. Therefore, you need to treat your tank as quickly as possible to prevent the illness from spreading.

Regards,
Chloe.