Temperature can be crucial to healthy fish. Marie, you posted in another thread about your neons dying, at 82F this is quite likely to occur. And SinCrisis, what fish do you have at 80+ F?
One of the things that must be considered when acquiring fish for a community (= more than one species in the tank) is temperature. This comes under the heading of water parameters. Fish in a tank should share very similar water [parameters. You cannot compromise. Some fish can "manage" within certain ranges, others cannot.
Temperature differences of only a couple degrees can be very significant to a fish. Fish cannot regulate their body temperature as we (mammals) can, so they are bound by their environment and their biological actions will change at different temperatures. If the variations in temperature are natural, such as cooling during darkness and warming during the daylight, there is no problem. But if the temperature is outside this range, the fish can be stressed which weakens the immune system, and this brings on health issues that would otherwise probably not occur. And a shorter life expectancy.
In our profiles the optimum temperature range is given for each species; optimum means this temperature range is best for this species. Some may tolerate higher or lower temperatures than the optimum range, but usually only for short period, not permanently.
Maintaining white clouds at "normal" aquarium temperatures speeds up their biology and leads to shorter lives and probable health issues along the way. Neon Tetra
occur in cooler mountain streams, 77F is the absolute maximum for this species to keep it in good health. Discus
and the common or Blue Ram
would suffer at this low a temperature. These are just random examples. It is vital for the health of the fish to have the aquarium temperature within the optimum range, and when combining different species this must be remembered.