One dead fish is "just one of those things" they do get heart attacks and bump themselves on the lid, etc. 2 dead fish is a trend. If you tank is less than 3 months old (or you have added more fish within that time) poor water quality is more likely than disease. Just when your ammonia is going away, suddenly nitrites can spike overnight and kill fish, then the dead fish causes more ammonia. Ammonia and nitrite both affect the gills and the fish have trouble breathing. Warmer water has less dissolved oxygen and medication reduces it further. Therefore, unless you have at least a general idea what disease is present, change water rather than medicate. Don't even think about adding more fish until 2 months have passed with no more deaths.
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