A properly selected aquarium water pump will have a flow rate that allows your inline filtration system to work its best. Your aquarium will stay cleaner longer, providing a healthier environment for your inhabitants.
For most aquarium systems, the water pump should be strong enough to turn over the total aquarium volume at least five times per hour. For example, if you have a 100-gallon aquarium, you will need a pump and filter rated at a flow rate of at least 500 gallons per hour (gph).
Pump Selection and Making Sense of GPH Rating
Since flow rate progressively decreases with each vertical foot water needs to travel, and most aquariums are generally three to four feet off the floor, a water pump selected at the minimum flow rate will already be slightly underpowered. In general, select an "oversized" or the next larger pump.
An oversized pump will compensate for natural reduction in flow rate caused by head height as well as elbows and sharp turns in plumbing. A larger pump with a higher flow rate can be adjusted with ball valves but an undersized pump cannot produce more flow than what it was designed for. While the listed pump gph rating can give you an overview of pump performance, refer to the pump flow rate chart to get a better sense of how it will function under different head height conditions.
Different pumps for different applications
The right pump with the proper flow rate can make a big difference in the health and happiness of your aquarium inhabitants. Research pump type and flow rate to make aquarium-keeping a much more enjoyable hobby.