I have a 20g tank with 4 neons, 5 sharpea, and 2 ghost shrimp. All of my fish are doing well except 1 neon. He has very labored breathing and very lethargic. No physical signs except becoming more dull, no spots no ich nothing of that sort. I have checked all of my water levels ie Nitrate, Nitrite, Amonia, PH, Temp and all were within normal limits. This fish has been fine for 4 months and just recently looks sick. I have in my QT tank but I don't know how to treat him and get him feeling better. Any Suggestion?