Most health-related issues regarding fish are related to poor water conditions. If the water in an aquarium is not suitable for the fish them problems will start arising. If any of your fish start showing signs of ill health, the first thing to do is a water test. A lot of people jump straight on the forum and starts asking questions about why their fish have suddenly stopped eating, started breathing heavily etc. With all the will in the world, it is very difficult to diagnose problems unless they are obvious. If a fish does start showing signs of ill health, you must test for a ammonia, nitrite, nitrate and pH. You can then post a thread on the forum asking for advice making sure that you tell us exactly what the readings are. These four tests will tell you a lot about what is going on in your aquarium. I suppose it’s a bit like going to the doctor and having your blood tested. Even if you don’t understand the test results, somebody on the forum will, and therefore will be able to advise on the situation.