I have had my Tilapia for about 3 weeks now with no problems. Today I have found 2 floaters. I inspected them and see no signs of abnormal growth or fungus. I test the water everyday and nothing shows up abnormal. Coincidence? Plenty of air (48"bubble tube) and none of the fish have been gasping for air. I'm going to hold off feeding a couple of days and see what happens. Any thoughts?