Trying to decide between a submersible and external aquarium pump ? While a submersible pump can be a complete breeze to install and generally a lot less expensive to purchase we all know they add heat to the water. So how much heat ? In this demo we attempt to give you a good idea how much of a difference this really can make. Depending on the tank size and other equipment on the tank it is very possible a wise decision here could help us avoid other costly pieces of equipment like an aquarium chillier. Disclaimer