Hi Tsarmina,I would keep an eye on this as it could be ICH or WhiteSpot, do any of the other tank mates have it?, would be good to know what your water parameters are, would be great if you could invest in a test kit, sooo much easier than having to run a water sample down to the LFS, picked up mine from Trade me, great investment, if you have any suspitions that maybe something is not right in the tank, you can test it there and then, and adjust whatever needs to be adjusted.
Good Luck
Lynda