I have a black molly that is 2 1/2 inches long. Late last night I noticed she had a small white cottony patch on the narrow area between her tail and stomach. The spot was probably about 1/2 of a centimeter. I put maracyn 2 into the tank and today the patch looks like it is starting to go away and much duller in color then before. I was just curious as to what it was. Thanks.