HOW AQUARIUM SUMP PUMP WORKS – Best sump, design and setup

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If you want greater control over your aquarium then you need a sump pump and you also need to learn how aquarium sump pump works best to maximise this control and take better care of your aquarium.

The benefits far exceed the risks, and thus most successful aquariums you’ll see utilize a sump.

So, what is a sump? A sump is simply a container to collect water from a plumbed system. So, what does that mean? It means that if you have tubes and pipes (plumbing) coming out of your tank to carry water to filters or other equipment, you may need some place for water to collect. This place for water to collect is your sump.

A sump is not an aquarium filter. While a sump may contain filters or may house other aquarium equipment, the sump itself does not provide any filtration for the fish tank.

Benefits derived from incorporating a sump into your current setup:

  • Increased total water volume – This dilutes your water of accumulating pollutants, and helps avoid issues that occur quickly in sumpless tanks.
  • Skims the surface – No more surface scum, just crystal clear water.
  • Lowers temperature – I’ve observed a 2° F drop after the sump is installed.
  • Hides equipment – Heaters, protein skimmers, monitoring probes, grounding probes and more can be moved to the sump & out of the display tank.
  • Consistent water level – The display tank will maintain the same water level all the times; evaporation occurs in the sump over time (see auto top-off).
  • Safe place to pour in additives – Adding chemicals or new (Reverse Osmosis De-Ionized) water in the sump allows it to mix before entering the display tank.
  • Increased circulation – The return water from the sump is yet another way to move water in your tank. You can point the return outlet(s) in different directions to create flow, instead of putting more powerheads in your display tank!
  • Increased oxygenation – As water drains into your sump, air mixes in the water, allowing beneficial gas exchange, releasing CO2 and adding fresh O2.

One thing that is important in determining whether you need (or even want) to get a sump for your home aquarium is whether your fish tank is an open or closed system.

Most aquariums are closed systems. In a closed system, there is no place for water to leak out. Canister filters, ultra-violet sterilizers, and fluidized bed filters are all closed systems.

Water is taken out of the fish tank through a tube, pumped through the sterilizer or filter, and returned to a point inside the tank. This is called a closed system because there isn’t any point along the water’s path where it is not controlled and contained. Closed systems do not need a sump.

Open systems have some means within the system where water could – or is even expected to – escape. Trickle filters and protein skimmers are open systems. These pieces of equipment are designed with openings to allow the release of water, air, or waste.

Because these systems are open, they need something to catch the water that can (or does) pass through. Though they can be set up so that this can fall back into the tank, usually it is the sump that catches this overflow.

Water is returned from the sump to the main tank. This is accomplished with a circulation pump placed in the sump (if the pump is submersible) or plumbed in adjacent to the sump (if the pump is not submersible).

In most cases, water is pumped from the sump into the aquarium, and then allowed to flow back into the sump. In this way, the pump is allowed to run continuously. In some cases, however, there may not normally be water getting into the sump. In these cases, the pump needs to be switched on and off as water collects in the sump.

This is normally accomplished with a float switch, similar to the floats that turned off the water in old-style toilets, or the switches that automatically turn wells back on when stock water tanks start to get low.

Sump Size
Since the main reason for having a sump set up with your aquarium is to keep water (or aquarium waste) from spilling out onto the floor, you need to make sure that your sump is large enough to do that in the case of a problem.

In general, this means that your sump needs to hold all the water that can drain out of the plumbing, filters, or anything else in the case of a power failure. That doesn’t mean that the sump needs to hold all the water in the tank too, the tank should not be able to drain in the case of a power failure. The sump just needs to hold all the water in pipes, plumbing, tubes, or other containers that allow water to flow into the sump in the first place.

Usually the easiest way to do this is to set things up and get things running, then turn off the power to the tank and let water drain into the sump. This will tell you how much water drains out of everything into the sump. While the power is still off, fill the sump close to the top. Then turn the power back on.

As water is pumped out of the sump and back into all the systems, you will see the water level in the sump go down. After everything has been running for a few minutes, maybe half an hour, you will see the level the water is lowered to in the sump. This is the HIGHEST level the water can ever be in the sump and not risk a problem in case of a power failure.

If the sump is the right size for the system you are running, you should have plenty of water still over the pump to allow for safe operation. (You will probably want to mark this level somehow so you know how much water the system can take.)

Remember, in a system with a sump, the overflow in the tank will keep the water level in the tank constant. Any water that is evaporating from the system will be missing from the sump, and if you are not paying attention to this level you can expose the pump and risk overheating or other problems.

Also remember that if you add water to the system, you will probably not see any meaningful rise in the water level in the tank – the rise in water level will be in the sump. Be sure to never fill it above the maximum level you determined above.

In addition to their primary purpose collecting water (or possibly waste) and preventing a spill or damage, sumps can also be used to house unsightly equipment, or equipment that needs to be out of the tank for some reason.

The most common use of a sump is in conjunction with a trickle filter. Generally trickle filters are set up to allow water to flow through the “tower” of the filter and drop into a sump. Water is then pumped back into the tank to repeat the process.

Sumps are often used to house protein skimmers, though many skimmers can be set up in the aquarium. The sump provides a location out of the fish tank for the skimmer, which can be both large and unsightly. In fact, the higher quality skimmers really can’t be set up in the tank.

By setting the protein skimmer up in the sump rather than out on its own, the sump then can act as a back-up in case you forget to check the catch as often as you need to.

Once people have a sump connected to their aquarium, the aquarium heater is often one of the first things moved to the sump. This can also be important if the aquarium houses particular aggressive of belligerent fish that may damage the heater.

However, you need to be aware that if the heater is in the sump, it is only indirectly heating the tank, so it is even more important to monitor the temperature in the sump and in the tank.

So how does it work specifically? – HOW AQUARIUM SUMP PUMP WORKS

Water drains from the display tank into the sump container beneath. The water is pushed back up to the tank with a “return” pump, which is either submerged in the sump or run externally (which involves bulkheads and plumbing, but avoids adding as much heat to the water).

As the water rises slowly in the display tank, it flows into the overflow box (or chamber), and this drains back into the sump. It is a constant cycle, and the goal is to pump as much as the tank can drain. Most people aim for 10 to 15 times the volume of the tank for total circulation.

The sump’s return flow would be a portion of that total circulation, maybe 3 to 5 times the total circulation, and the rest is provided with powerheads and/or a closed loop system.

The way it works
 is that there is a baffle on the inside and one on the outside, to keep the ‘bubble’ of water trapped in that center zone (the inverted U) until flow is restored. If it has a leak, air will bleed in and water will go out, and the siphon is lost. So it has to be tested with water after it has been built.

Take it to the sink, thread or snake in a piece of airline tubing into that chamber, and while water is filling the inner box, you suck out the air with your mouth on the end of the tubing. Then you watch it closely, to see if any airbubbles start bubbling up inside that chamber. If you see none, it is perfect. See this page for info about building your own.How does a weir, or overflow box like the above work?

To establish flow rates, you have to get a pump that will match how fast the drain will flow. I have a 1″ drain on mine, and because there is no volume of pressure over that drain (or bulkhead), my maximum flow rate is 300gph. If the bulkhead were at the base of the tank, and I had gallons of water pressing down due to gravity, it might drain as much as 600 gph. But that is not the case. In the outer box of the weir, there is maybe a pint of water, so it goes more slowly. You want to find a return pump that will match your drainline, but you also have to figure head pressure as well. How far does the pump have to push water back up to the top of the tank to refill it? The submersible pump in the sump under my 29g has to push water straight up 5 feet. So a Mag 5 at 5′ pumps 300gph. A perfect match!

To avoid too much flow to your tank, in case your pump is too powerful, you can put a “tee” in your return plumbing, and an elbow pointing straight back down into your sump. Then you put a ball valve on that. If the valve is wide open, the majority of your water will go straight back into your sump. The more you close the valve, the more water goes up to the tank. This is the best system, because your pump will never feel a restriction and it won’t shorten the lifespan of your pump.

What is a return line?   Is that just a pipe going up?

The return line is the plumbing used to get the water back up to the tank. Rigid pipe is preferred, with a minimum of 90° elbows. The return line needs to have holes drilled in it to prevent excessive water from being siphoned out of your display. (See next point for more details)

How do I prevent a flood? I don’t want the sump to overflow and ruin my floors (or carpet)!

To avoid your sump overflowing it must have room for excess water. When your sump is running, as water drains down from the tank, it is pumped back up. When the pump is off, some water will drain down into the sump. This will be water from your drain line, from your return line, and from the tank (which is determined by the depth of the weir/overflow inside the tank and how deep your return line is in the tank).

You need to drill two small 1/8″ holes in your return line, 1/2″ below the water’s surface when the tank and sump are running normally. These holes are referred to as a siphon break. When the pump is off, water is sucked out of the tank by the return line, but as soon as the water level reaches those holes, air is sucked in and stops any more water from being siphoned out of your display tank.

Two holes are better than one, in case it clogs or a snail decides to park on the hole at the worst moment possible. Typically, you will only have 2 or 3 gallons drain down when the pump is off, so make sure there is enough room in your sump to hold an extra 3 gallons or more.

Mark your sump’s water level. The return section of your sump (typically after the bubble trap — explained above) will fluctuate as evaporation takes place. So when your sump is set up and running, turn off the pump. The tank will drain into your sump a little, and you’ll note how much water has accumulated.

If you have room for more water in the return area, add more. Turn the pump back on, and observe where the water level is in that section now. That is your maximum level. Mark that spot with a line, a piece of duct tape, whatever. Then when you top-off your sump with fresh water, never add more water than that line. Because if you do, and the power goes out, your sump will overflow.

How can I keep fish and snails out of sump?

Most overflox boxes come with “teeth” that prevent small creatures from entering the weir and drain system. However, snails don’t care about barriers, and will climb out into the air to get to their next target. Observing snails in my overflow, they clean up the algae and crawl back out.

Some may find a way to get deeper into the plumbing, and you may see one traveling down inside your drainline (if it is clear flexible material), seemingly unaware of their destination or current location. As long as they aren’t an obstruction to your flow of water, it doesn’t matter. The only place you must keep them out of is the intake of your return pump. I have snails in my refugium keeping the surfaces clean so I can see inside, but if one is in my return zone, I pull it out and put it back in the refugium.

Fish tend to stay in your display, but occasionally one will decide the amphipods are too delicious looking to not go for it. My Yellow Coris Wrasse has jumped through the teeth of the weir and had a fantastic time devouring every one of those pods. Before I could “rescue” him, he hopped right back out into the main tank again.

Others have lost a fish for long periods of time, only to find them in the overflow. Others have discovered their loved pet in the sump! You can put a plastic screen over the surface of the overflow, like what is used to keep leaves out of gutters.

5 Best Aquarium Water SUMP Pumps: (2020 Reviews & Guide)


1. KEDSUM Submersible Ultra Quiet Water Pump

KEDSUM Submersible Ultra Quiet Water Pump


First, we’ll take a look at the KEDSUM submersible water pump. This pump is suitable for both freshwater and saltwater tanks and can be installed with suction cups vertically or horizontally on the sides of the tank or walls of the pond.

This pump definitely packs a punch despite its small size, as it functions at a powerful rate of 660 GPH or 3,000 liters an hour. The KEDSUM water pump is also very energy-efficient and is ideal for tanks and ponds because it can be easily hidden or placed out of site due to its small size.

The only thing going against the KEDSUM water pump is the fact that it may not be suitable for the sensitive fish in your tank or pond because it requires a little lubrication to function properly.

If your fish are still very young or are just more sensitive naturally, you may want to keep an eye on them during the first couple of days of using this water pump. HOW AQUARIUM SUMP PUMP WORKS


  • Quiet operation
  • Can be installed quickly both vertically and horizontally
  • Energy-conserving


  • Inner shaft of pump needs lubrication; not suitable for sensitive fish
  • Needs maintenance from time to time

2. Homasy Upgraded Submersible Water Pump

Homasy Upgraded Submersible Water Pump

Next, we have the Homasy submersible water pump. This pump is also very powerful and runs at a great rate of 400 GPH.

It’s suitable for use in tanks, fountains, and spouts and hydroponic systems. It also comes with a warranty of 12 months in case you find something out of order.

The Homasy water pump is a good choice if you’re looking for a pump that works well, even in low water amounts. It can run up to 48 hours with dry burning, so you don’t have to worry about your pump malfunctioning if you’re gone for a few days and can’t add more water to the system.

The problem with the Homasy water pump is that it can easily get clogged or blocked by large debris, which why it’s necessary to detach and clean the shafts and filter once every month. The pump also uses less power to push the water, making for weaker flow and currents. HOW AQUARIUM SUMP PUMP WORKS


  • Dry burning capacity
  • Warranty included


  • Requires maintenance every month
  • Weaker power in pumping

3. Simple Deluxe 1056 GPH Submersible Pump with 15′ Cord, Water Pump for Fish Tank

Submersible deluxe pump has a Pre-filter on the intake that prevents debris from entering your pump and extend the life of your pump, Max flow rate: 1056 GPH, Max Lift Height 12ft

The Polished Aluminum Oxide Ceramic Impeller Shaft insures long pump life because it is non-corrodible and more than 3 times as hard as stainless steel. Epoxy Resin Encasement of key internal motor components prevents unwanted conductivity and corrosion of metal parts

It is Safe for fish with no exposed copper. Easy to clean with no tools required to disassemble and clean filter/impeller. The Electric Cord is waterproof, 18# gauge copper wire, molded plug with ground, heavy duty flexible vinyl jacket, resists oil/grease/moisture, abrasion resistant and very good flexibility at all temperatures. HOW AQUARIUM SUMP PUMP WORKS

This water pump easily Circulates and aerates the water, making it more attractive to your fish or turtles. This submersible pump is perfect for aquarium, fountains, spout and hydroponic systems

4. VicTsing Submersible Water Pump For Aquarium

VicTsing Submersible Water Pump For Aquarium

The VicTsing submersible water pump is also a good contender for an aquarium pump. This pump offers more customization to how much pressure you want to have in your water flow through the filter. There’s an easy-to-use turning knob that lets you control the water flow.

The VicTsing water pump is also very small and easy to conceal in your aquarium, and operates very quietly, adding to the easy-to-hide nature of the water pump. It’s a good pump to start off with if you have a small tank because it’s simple to install and understand its functions.

It’s important to mention that the VicTsing water pump has a low rate of 80 GPH, so if you have a larger fish tank, this may not be the right pump for you.

It also requires maintenance every month, so that’s an important thing to consider if you’re busy and don’t have extra time to clean the pump.


  • Very small design, easy to conceal
  • Simple design makes it ideal for new fish owners
  • Controllable water flow function


  • Low GPH rate
  • Monthly maintenance

5. Tiger Pumps Submersible Water Aquarium Pump

Tiger Pumps Submersible Water Aquarium Pump

Next up is the Tiger Pumps submersible water pump. This pump is designed to work well underwater and can be placed vertically or horizontally on your tank.

It’s got a pretty good pumping rate at around 120 GPH and is easy to install and detach when it comes time to clean the filter and shafts.

A big plus for the Tiger Pumps water pump is that it comes with a money-back guarantee, so if it doesn’t work out for you, you can get a full refund for your money. HOW AQUARIUM SUMP PUMP WORKS

The Tiger Pumps water pump makes a good addition to any pond or aquarium, but as with a lot of the pumps mentioned, it requires monthly maintenance. That can be a drag if you don’t have the time to clean the pump every month but is otherwise expected.


  • Money back guarantee
  • Good flow rate


  • Monthly maintenance
  • No dry burning function despite good flow rate


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