Yes, it does depend on what kinds of fish you have and the needs of each, there are a wide variety which can be called tropical though groups of fish as mentioned prefer different temps some around 74F and some above 80F. 78F is the usual default though.
As for the heater - if you have one, turn it down a degree at a time, say 24 hour period. Sometimes the water temp goes up because it's hot in the house or because the light is heating things up. Try to avoid direct sunlight shining in.
Some fluctualtion should not be a big deal but if it is due to the heater, just turn it down a little. Some fish are sensitive so it helps to know a lot more about each fish variety you have and then decide if they can all be in the same temp tank or if one or maore varieties would be better rehomed or in a specific for them type tank.
Being in the wrong temps can cause issues with the fish and result in illness.
