What Size Return Pump Do I Need?(The Definitive Guide)

What Size Return Pump Do I Need?


what size return pump do i need


This is the ultimate guide to choosing the right size return pump for your saltwater tank.

In this comprehensive guide I will cover:

  • How to choose a return pump
  • Return pump vs tank size
  • Types of return pumps
  • Pump maintenance
  • And much more


Once you have decided on a sump system for your saltwater tank, you are going to need some equipment to set it up properly. One of those things you will need is a return pump. But which one should you buy? There are a few different things to consider before you make the decision.

How to choose a return pump for your saltwater tank


Here is how to choose the right size return pump:

  1. Determine the maximum flow of your overflow drains.
  2. Calculate the desired turnover rate. The normal rate should be 5-10x your water volume.
  3. Calculate the head pressure and height, match it to the flow chart of the desired pump. Keep in mind plumbing diameter is a factor.
  4. After your calculations, make sure the pump flow is not higher than your drain flow.
  5. Your return pump flow can be reduced but can not be increased.

That’s it! Keep this a simple process. Many people over complicate it and end up buying the wrong return pump. At the end of the day, as long as the pump doesn’t push more water into the tank than drains from it your all set.


Let’s look into this a bit further:

1. Determine the maximum flow of your overflow drains

Depending on your bulkhead size, you need to check the gravity flow of water draining to the sump. This will depend on the number of drains and size of the drains. A commonly used size for aquarium plumbing is 1″. You can use other sizes but this is the most popular size. On average, a 1″ drain will flow 960 GPH. If you have dual overflows, then the flow would be double. If you are using a hang on the back overflow box, the flow rate will be given from the manufacturer. For example, the Eshopps PF-800 has a maximum flow rate of 800 GPH.

Use this chart for reference.


2. Determine the required turnover rate

You should aim to have a turnover rate of 5-10x your water volume. So let’s say you have a 100-gallon aquarium. You will want to choose a return pump that will push between 500 and 1000 GPH back to your aquarium. I prefer to use the lower end side of that number.

*Pro-tip – If you have a protein skimmer in your tank, you will want to keep the flow rate on the lower end as the skimmer will be more efficient. You don’t want to push too much flow through your sump.


3. Calculate head pressure

In order to calculate head pressure, you need to look at your plumbing and determine how many feet your pump needs to push the water. Return pumps will have a flow rate at 0 head pressure and incorporate a flow chart to determine the reduced flow given a certain height.

Most aquariums will have about 5-6 feet of return plumbing. In order to calculate the reduction in head pressure, use the following rules of thumb:

1 foot of vertical plumbing = 1-foot head pressure

Every 90-degree elbow = 1-foot head pressure

Every 10 feet of horizontal plumbing = 1-foot head pressure

As an example, if you need to pump water 5’ vertically, through 3 elbows and a 10’ horizontally, your pump will be under about 9’ of head pressure.

Looking at your desired return pump flow chart, you can determine the flow.

This chart is for a Mag Drive return pump. As you can see, the flow rate at 9′ of head pressure is 500 GPH for the Mag Drive 9.5 pump.

Aquarium turnover rate calculator

For example:

Danner Supreme Aqua-Mag 9.5 Water Pump produces 950GPH. In our example above, it will produce 500GPH at 9 feet head pressure. If we have a 100-gallon tank we can calculate 5X turnover rate which is sufficient.  500/100=5

If you want to determine the time required for a pump to process a specified percentage of an aquarium system’s water, use this calculator.


4. Make sure your return pump flow is not higher than the drains


Using our example, if we have a 1″ drain on our tank at 960 GPH and at a head pressure of 9 feet, we can expect the Mag drive 9.5 to return 500 GPH which is exactly 5x turnover rate for our 100-gallon tank. Perfect!

If you are using a hang on the back overflow box like the Eshopps Pf-800, we can still use the Mag Drive 9.5 pump as the maximum flow from the overflow box is 800 GPH and the return flow is 500 GPH.


5. Always keep in mind that your return pump flow can be reduced

You can choose a DC pump that has a controllable flow. If using a constant speed pump, you can also add a ball valve to the plumbing and dial down the flow if you find it too much. It is easy to match the exact drain and return flow with precision.

One thing you can’t do is increase the flow of the pump. If it’s a constant speed pump, you are stuck with what you have. If you need more flow, you will need to buy a new pump. So choose the pump wisely!



Why do you need a return pump?


A return pump is needed to return the water that drains into a sump tank back into the main display.


Where do you place the return pump?


Most sump systems will have a return pump section built into them. This is where the pump goes. If the sump does not have a return section, then it will go somewhere in your sump generally after the protein skimmer.

How do you reduce noise and vibration from a return pump?


This is a common question and if you are anything like me, I can’t stand the sound of a return pump on my tank. Vibration can cause noise throughout your plumbing which can be annoying. Luckily there are several return pumps on the market today that are almost silent.

But if you have one that is vibrating or making noise, there are a few things you can do to help.

  • If your return pump comes with rubber feet, make sure you install them. This will help dampen the vibration.
  • Flex tubing will be much quieter than rigid PVC if you have a noisy pump.
  • Some people add silicone tubing from the pump to the PVC to help reduce noise and vibration
  • Use a silicone vibration silencer. They are designed for return pumps and do a great job.
  • If all else fails, you can use a silicone pot holder from a kitchen or hardware store to place under your return pump. It’s a cheap fix!


How much flow does a 75-gallon reef tank need?


If you have a 75-gallon tank, you should aim to have between 375 and 750 GPH. This is using the 5-10X turnover rate normal rule of thumb. Remember to take into consideration total system water volume and not just tank size.

What are the operating costs of a submersible saltwater aquarium return pump?

On top of the initial purchase price of the return pump, they also will cost you money to operate. Depending on the model you are using, the cost will vary. Some pumps will use more energy than others. So take this into consideration before buying a return pump.

The average operating cost per year of a return pump will be around $100 per year. But that can vary quite a bit.

For example, the Danner Mag Drive 9.5 has a power consumption of 93 watts. Assuming electricity costs $0.12 per kilowatt-hour and the return pump operates 24 hours per day and 7 days per week, this pump will cost $97.80 per year to operate.

Using the following calculator from Marine Depot, you can see the results. You can check out their aquarium electricity calculator here.


I have put together a table that shows the operating costs for various return pumps. As you can see there is a wide range of costs depending on the model. These numbers are based on the manufactures info. Assuming electricity costs $0.12 per kilowatt-hour and the return pump operates 24 hours per day and 7 days per week.

All of these pumps are available on Marinedepot.com here.

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Types of return pumps


Internal vs External Return Pumps


Most of the return pumps on the market are designed to be installed inside a sump or plumbed externally from the outside of it. There are pros and cons to both.

Internal return pumps are great for sumps that are placed inside a stand. With a few feet of plumbing, you are able to return water from a sump back to your tank easily. If you need to pump water from an external location that is a fair distance away,  you will need to use an external pump as from a remote location you are pumping water a greater distance.

The disadvantage of using an internal pump is that it will put any heat it creates back into the water. Not really a huge drawback. Most external pumps will have a cooling fan so that is not an issue.

AC vs DC Pumps

Many return pumps in the hobby are AC operated which are basically plug and play. Most will have no option for controlling speeds or different modes. They just plug into the outlet and that’s it.

The market today is seeing a huge change and the development of DC pumps is growing. These pumps plug into the wall outlet as well, but they are connected to a controller that adjusts the electrical AC to DC.

The benefit to using a DC return pump is that the speed of them can be controlled. Plus many pumps will have various modes available such as feed mode.

Most of the DC pumps have their own App you can use to completely control your pump remotely using a smartphone or other device.