What is the ammonia, nitrite, nitrate and pH of the aquarium water?
Was the fish in a tank with other types of fish when you got it?
How long has the tank been set up for?
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It looks more like excess mucous but could be white spot.
Do a 75% water change and gravel clean the substrate every day for a week and see if it helps.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
Post pictures if it changes.
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TREATING WHITE SPOT
Triple Sulpha can treat white spot if that is the problem. However, male Siamese fighting fish (Betta splendens) do not normally get white spot because they are not normally kept with other fish.
Triple Sulpha is also safe for invertebrates (shrimp & snails).
Heat can be used to treat white spot. You simply raise the water temperature to 30C and keep it there for 2 weeks, or at least 1 week after all the spots have gone. Then reduce the temp.
Before raising the temperature, do a big water change and gravel clean the substrate. this helps remove some of the diseases/ parasites in the water and provides a cleaner environment for the fish.
Increase aeration/ surface turbulence when using chemicals, salt or raising the temperature because they all reduce the oxygen level in the water.
Remove carbon from filters before using chemical medications ( like Triple Sulpha) or the carbon will remove the medication form the water and the fish won't be treated.
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To work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.
When you measure the height, measure from the top of the substrate to the top of the water level.
If you have big rocks or driftwood in the tank, remove these before measuring the height of the water level so you get a more accurate water volume.
You can use a permanent marker to draw a line on the tank at the water level and put down how many litres are in the tank at that level.
There is a calculator/ converter in the "FishForum.net Calculator" under "Useful Links" at the bottom of this page that will let you convert litres to gallons if you need it.