How to make a sump for a fish tank

Updated February 21, 2017

Saltwater aquariums and saltwater filtration systems can be hard to maintain. However, If you have more than one saltwater fish tank you can keep both aquariums clean using a sump system. A sump system is a water cycling filtration system. A sump system allows the water to cycle through three different aquariums. One of these aquariums filters the water and then pumps clean water back into the other, which makes it much easier to care for your saltwater fish and your saltwater fish tank.

Take the smallest of the three aquariums and make it the sump filter. You can start with more aquariums than just three but no less than three. The point is to get clean water to cycle through two aquariums and then out to get filtered in the sump aquarium.

Divide the sump into three compartments by using the two partitions.

Fill one of the three compartments with sand, rocks, carbon, carbon packets or any other kind of filtering device that you wish to use. A combination of more than one filter would probably work best.

Mix salt and water to make the desired saltwater for you salt water aquarium. Make sure that you get enough salt water to fill all three aquariums so if you have a 40-, 20- and 10-gallon system, make sure you have 70 gallons of water mixed. You can use the aquariums to mix the water if you don't have any place to put that much saltwater.

Fill the sump with water.

Place the water heater into the second compartment of the sump. The first compartment will be the filter, the second compartment the heater and the third compartment will be the clean, warmed water.

Cut a small, no more than two inch, rectangle on either the left or right side of the largest of the two aquariums.

Add a lip to the cut you've made. This will act as a "waterfall" into your second largest aquarium.

Place the aquariums on a large enough table that can fit the two larger aquariums on top and the smaller, sump, on the bottom.

Set Up both of the aquariums. If you need help with this section, research "how to set up a saltwater aquarium." Make sure that you ignore any instructions about putting in a filter or putting in any livestock.

Put one of the two pumps into the second largest aquarium. Make sure that you have enough pipe to reach down into the filtering compartment of your sump.

Put the second pump into the sump's clean water compartment. Make sure that you have enough pipe to reach up to your largest aquarium. The first pump will pump dirty water down to the sump for filtering and the second pump will get clean water from the sump up to the largest aquarium. When the largest aquarium overflows the lip, clean water will fall to the second aquarium.

Set the pump speed on both pumps so that none of the aquariums overflow. This might take some trial and error so make sure that there is nothing that cannot get wet around your aquarium set up. Add your saltwater fish and enjoy!


The more aquariums you have, the more difficult things get, so make sure you don't expand your hobby too quickly.


Keep all electrical connections away from the aquariums and away from the floor. Check saltwater fish regularly to ensure they appear healthy in their environment.

Things You'll Need

  • 3 different-sized aquariums
  • 2 pumps
  • 2 partitions
  • Rocks
  • Carbon
  • Water Heater
  • Water
  • Salt
  • Saltwater fish
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