Doug E. Fresh said:What are some problems that a fish not eating for a day or two would be one of the first signs of?
Too be honest, a fish not eating for a day or two could be a sign of just about any problem a fish could have. Most fish will eat until the food is gone; they don't get hungry/full the same way we do. Some fish don't eat all that much (that you can see, at least) For example, I've got a weather loach that hides most of the time, so I don't see him eating very often. But, where you said your fish started of eating vigorously, then stopped eating, you most likely have a problem.
In general, unless the fishes' problem is obvious, (IE, bleeding, torn fins, white specks all over em ect..) it can be really hard to tell what is wrong with them. For this reason, we here at the forums always ask for test kit results on your tank, how long it has been set up with fish in it, ect. Particularly Ammonia, (NH3) NitrAtes (NO3) and NitrItes (NO2). The others you see talked about are less important. (pH, for example is not too critical for most fish, as long as it doesn't change much.)
About the "Aquasafe" stuff you refered to: I'm not familliar with the product, I would assume it is a chemical you add to the water to remove Chlorine and ChlorAMines. If you have municipal water (IE: unless you have a well) Then you should use it as the package says to. If you are SURE you only have chlorine in your water supply, and are sure you DON'T have chloramines, (most people do, unfortunately for the fish) You can get away with not using the Chlorine remover if you let your water sit in a clean plastic bucket for a day or two. Chlorine will dissapate from the water on its own. Chloramines, on the other hand, will not go away. (at least not quick enough to do us fish keepers any good) You could ask whoever supplies your water if they put chloramines in it.