Sounds like you may have a couple issues here. First, I'd say your tank is actually somewhat nutrient starved. Without consistent food inputs your pods, beneficial bacteria, and other critters have waned overtime. This prevented your clowns from foraging all the time and made your aquarium less stable. Clowns are actually pretty active fish and consequently require higher metabolic (food) requirements. Again, not having consistent access to food caused them to become stressed and this allowed them to become more susceptible to disease. My advice would be to start feeding smaller portions more frequently and purchase a reliable autofeeder for when you're away. Also, you may also be having problems with oxygen saturation. My old nanocube developed this oily surface scum; which inhibited gas exchange. I also noticed that my fish would appear pale and breath heavily for about an hour or two after the lights came on- symptoms of anoxia. A simple airstone resolved both issues. The Bio-enzymes wouldn't cause infections in fish. A lot of those products tend to be mostly water with little or no active ingredients. Swapping out a few pieces of your liverock for new high quality stuff would be much more beneficial.
