I have had my clownfish for about 5-6yrs with no problems until about a week ago it's belly got very large. Today I noticed a clear sack u dear the fish. It seems to be swimming normal for the most part and seems to be eating fine. It is in a 30gallon biocube and the water tests are normal. I went to the local pet store but the fish guy said he had no clue as to what the problem could be. Here are a few pics please help.