If your fish have red spots on the skin surface anywhere. Most cases it is too much ammonia in your tank. Do you change your water weekly? If you do, do you stir the gravel? This is mainly for GF. They are very dirty dudes, and they need alot more h2o changes than you would think.

The water in my tanks gets changed weekly. I vacuum deeper depending on the tank. The more heavily planted the tank, the more I just disturb the surface slightly every few weeks. Otherwise, I just change out the water only and rinse out the filter media. For the tanks with Cichlids and Catfish and that have only a few plants, I vacuum a bit deeper into the gravel. The amount of water that gets changed out varies on the tank. The messier the residents, the more water that gets changed out. That is, it ranges from 25 to 30%. I have one tank that I am considering changing 25% twice a week. I have not had an ammonia problem for some time, since cycling. Now it is a matter of keeping the nitrates down. I even tried going filterless for a while, but the bio-load (fish specifically( in my tanks is too high, compared to the number of plants. My two smallest tanks with plants and snails only are filterless.

:D doesn't sound like you have a problem then. What type of snails do you have? to have them filterless? they must be pond snails?

I don't like keeping live plants, so I don't have any. I vacuum the gravel with a syphon tube while removing about 1.5 gaollons on my 10 gallon, and 4-6 gallons on my 29 gallon. I usualy do this every 1-2 weeks depending on the nitrate readings. I like to keep my nitrates 5-15 ppm. Both of my tanks are fairly lightly stocked.

Most important thing is how well your tank is cycled and what kind of tank residents you have.

Yeah, pond snails, ramshorn and sometimes a mystery snail.