I was thinking the same thing. It is diffacult to tell from the pix and I agree a side shot might help. Could you also post water perameters ammonia, nitrites, nitrates, Ph and temperature. The tank looks like a good candadate for Columnaris, the combination of warm water and lots of airation creates a suiteable environment for this to take hold. The best first line of defence untill we can make and educated guess as what it might be would be to do a 50% water change, lower the temp as suggested by duanes and add 1 tablespoon of salt per 5 gallons of water. If it is Columnaris this will slow it down untill you post additional pix and get your water perameters. Water parameters are important to determine the best medacation to use.