How long has the tank been set up for?
How long have you had the fish for?
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Check the water quality for ammonia, nitrite, nitrate and pH.
Do a 75% water change and gravel clean the substrate every day for a week.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
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The floating could be from too much air, which they swallow when taking dry food from the surface. Or it could be a swim bladder problem.
Stop feeding dry food for a week and feed frozen or live foods instead. If the problem fixes itself, then it is air in the intestines.
If it doesn't get better, then the fish has an internal problem that cannot be fixed.
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What are the tank dimensions (length x width x height)?
What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
Depending on what the GH of your water is, will determine what fish you should keep.
Angelfish, most tetras, barbs, Bettas, gouramis, rasbora, Corydoras and small species of suckermouth catfish all occur in soft water (GH below 150ppm) and a pH below 7.0.
Livebearers (guppies, platies, swordtails, mollies), rainbowfish and goldfish occur in medium hard water with a GH around 200-250ppm and a pH above 7.0.
If you have very hard water (GH above 300ppm) then look at African Rift Lake cichlids, or use distilled or reverse osmosis water to reduce the GH and keep fishes from softer water.