Sump Design by NVR Staff

The following information has been compiled from various sources and is intended to be an informative resource for anyone who is interested in setting up a sump. There is no absolute right and wrong in this hobby; opinions and practices may vary.

Section Headings:

What is a Sump and why do I want one?
A sump is a secondary tank that usually resides below the display tank, within the stand. Both tanks are interconnected with piping and a pump. Using a sump has several advantages:

  1. Increase Your Water Volume: The more water you have in your system the more stable it is.
  2. Equipment such as your protein skimmer, heaters, thermometer, filters, etc… can all be placed in your sump - out of sight.
  3. Provide a place to set up a refugium. The purpose of a refugium will be explained later.
  4. Provide easy access for doing water changes.

How does water get down to the sump, and how does it get back into the tank?
The water going to and from the sump follows a path, much like a circle. Imagine your tank full to the top with water. Now imagine what will happen if you put 1 more gallon of water into your tank - one gallon will overflow as you pour it in. This is exactly what happens when you use a sump, but of course the overflowing water goes to your sump, not the floor! This happens by way of an 'overflow system', and the water returning to the pump is handled by a 'return pump' at the sump.

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Types of Overflow Systems
An overflow system is pretty simple. In a 'reef ready' tank the overflow is built into the tank. It usually looks like a box and inside of it there are one ore more pipes that lead out the bottom of the tank and into the sump. If your tank doesn't have a built in overflow, don't despair - there is another option. You can purchase a device called an external overflow box. It hangs on the back of the tank and works by siphoning water up and out of the tank.which works by siphoning water out of the tank.

Both overflow types are usually reliable, however there are a couple of things to be aware of. If a fish, snail, urching, or other rouge critter becomes lodged in your overflow it may become blocked. If this happens there is a potential for a flood. If you're using an external overflow another thing to be aware of is that you need a way to start the siphon after a power outage. This is usually done with a small powerhead or vacuum pump that is located in the sump and attached to the high point of the overflow box.

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Avoid a Flood!
If you're designing a sump (or buying one) be sure to check that your design will prevent or at least minimize the chance of a flood happening. The 2 major causes of floods are:

  1. The overflow pipe (or siphon tube) becomes partially or entirely blocked while your return pump continues to pump water into the tank causing a tank flood.
  2. The amount of water above the overflow level in your tank is more than the amount of empty space in your sump, causing a sump flood.

To address issue #1 try to screen your overflow pipe off from snails, fish, or anything else that might find it's way into the pipe and block it. If your tank is reef ready then it has an overflow compartment which will keep most critters out of your overflow. If you're using a siphon tube then you may want to screen it off with 'egg crate'.

To address issue #2 you need to make a few calculations.
  1. First you need to measure the length and width of your tank in inches.
  2. Now assume that the normal water level in the tank will drop about 1.5 inches when the return pump is turned off and it drains into your sump. (If you know the water level will drop more, use that distance in your calculation).
  3. Multiply the length x width x 1.5 inches (or by the number you figured above).
  4. Divide the result by 231. This is the number of gallons will drain into your sump. Write this number down so you don't forget it. To determine how many inches this will raise the level in your sump do the following:
  5. Multiply the sump length x width (in inches).
  6. Divide the result by 231
  7. Now take the number you wrote down and divide it by the result above above and this will tell you how many inches the water level will rise in your sump.

Example:
  1. You measure your tank and determine it is 48" x 18".
  2. We'll assume the water level will drop 1.5 inches when the power is off.
  3. Multiply Tank LxWx1.5 = 1296
  4. Dividing by 231 = 5.61 gallons - write this down.
  5. You're planning on a sump with a measurements of 36" x 12", Multiply LxW = 432.
  6. Divide by 231 = 1.87
  7. Dividing 5.61 gallons (the number you wrote down) by 1.87 we find out that the water in your sump will rise 3 inches when your turn your return pump off.

To add a safety factor plan to leave at least double the distance the water will rise from the 'running water level' (see diagrams below) of your sump to the top of the sump. This will give you a little extra volume too, which will come in handy.
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How Big Should the Sump Be?
You may need to play with some different tank sizes on paper to find out exactly what will work for your sump. Some considerations are:

  1. How high will the water level rise when power is cut? Make sure the sump is tall enough to give you double this number, in addition to the depth of water that you want.
  2. Make sure the sump will be large enough to fit the skimmer you plan to use (if using an in-sump skimmer).
  3. A sump that's too tall may be hard to work in, plan accordingly.
  4. With all of the above considerations get the largest sump that fits the bill.

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What are the dividers for in a sump?
Most sumps have one or more sets of dividers known as 'baffles'. Their purpose is to not only separate different sections within the sump, but also to help prevent 'micro bubbles' from entering the return pump. When micro bubbles make their way back into the tank they are visually distracting and can be detrimental to the health of some animals. The design examples below will give you some ideas on divider placement.
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Examples of Sump Designs
Below are two examples of basic sumps.



  1. Overflow pipe from display tank: Water flows down this pipe into. This creates some bubbles as the water and air mix on the way down. Usually submerging the end of the overflow by 2-3 inches helps keep it quiet and running smoothly.
  2. Skimmer Section: The protein skimmer usually resides in the same section as the overflow pipe. The skimmer also produces micro bubbles.
  3. Baffles: This set of baffles acts as a divider to the refugium section (explained next) and as a bubble trap. Water is forced to flow downwards while air naturally rises, thus removing some of the bubbles entrapped in the flowing water.
  4. Refugium Section: Some hobbyists prefer to keep a refugium. The purpose of this can vary. Once common use is to grow macro algae that will compete with algaes growing in the display tank. It also provides a predator free place for copepods and other small critters to grow.
  5. Baffles: The up-down-up baffle draws in water from the bottom of the sump, where bubbles are least likely to be, water then travels up and over the middle baffle. Finally the water must make it's way down again. In this case there is some 'waterfall effect' since water is flowing into the pump section where evaporation takes place. To minimize air being re-introduced by waterfalling one approach is to loosely fill the last baffle section with live rock rubble.
  6. Return Pump Section: This is where the water is pumped back to the display tank by either a submersible pump or external pump connected with a bulkhead. The effect of evaporation is seen here because this is where water is being constantly drawn from so the water level will vary unless you use an auto top-off system.
  7. External Return Pump: Can be connected via a bulkhead. Using external pumps reduces the amount of heat that is transferred to the water.
  8. Lower Water Level: The water level of all other sections of the sump (and display tank) will remain constant. When water is removed from the system, either by evaporation or other means, the level will vary in this location. The larger the return pump section the less the level will vary, don't make this section to small or you will constantly have to add top off water to keep your pump from sucking air.
  9. Running Water Level: This is the water level of your sump while in normal operation. You should determined where this level should be using the information above. Any baffles that connect to the bottom of the sump should rise to your planned running water level. Baffles that are raised above the bottom of the sump should extend an inch or more above the running water level. When starting up for the first time you can add water as the pump is running until the water level is correct. You always increase your running water level by adding more water (keep in mind flooding considerations) but you can not decrease your running water level with alteration to the baffles connected to the bottom of your sump.

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Build One!
It is not difficult to do. Start with a new or used glass or acrylic tank. Either have a glass shop or plastics shop measure and cut the baffles. You can glue them in place yourself or have them do it. If you want an external pump, bring the pump and bulkhead with you and have them measure drill a hole for the bulkhead, you can do this yourself too, it's very easy with acrylic. It's probably wise to seek advice before starting any construction from other's who have done it. Of course there is always the option of buying a pre-built (or custom built) sump from a retailer. Some folks settle for a plain old rubbermade tub, just about anything will work really!
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Summary
There is definitely more going on with a sump than just a box of water. If done right you won't find yourself fighting problems. If done wrong it can be a major headache. Hopefully this will help you in planning your sump design. Good luck!

If you have any questions about sumps feel free to ask some fellow reefers


Happy Reefing!



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