If your fish need to be above 75 degrees you will need to purchase a heater for your fish tank. 

If you worry about your temperature going up or down by more than 2 degrees per day, you can purchase a heater.

You will be able to set the heater to come on when the water drops below a certain level.

If you want to lower the temperature you will need to purchase a chiller.  A chiller will cost you around $150-$200.

You want to purchase a heater which fits your tank’s size.  Do not purchase any heater because you will over-heat or under-heat your fish tank.

Never purchase a glass heater because it will shatter if you remove it from the water while it’s plugged in or hot.

You don’t want to have shattered glass at the bottom of your fish tank.

Always purchase plastic heaters.  Marineland makes a lot of excellent heaters that you can purchase.