Sump and overflow box setups

Most importantly, all of this has to happen continuously and simultaneously. Although logic says this is what is needed, in reality it could never happen successfully. For this concept to work, both pumps would have to move exactly the same amount of water constantly. Even if someone could get this to happen at any given point in time, it would never happen constantly because pumps get dirty at different rates and build up calcareous scale deposits at different rates, and a number of other changes occur that affect their outputs differently at different times.

Luckily for us there is gravity, which eliminates the need to pump water to the sump. Figure 2: Water can never be pumped to and from the sump at the exact same rates. This would result in either the display tank overfilling and the sump pump running dry, or the pump moving water to the sump operating at a higher rate and slowly draining the display and overfilling the sump. There are two common ways to get water from the display tank. Both allow for a constant water level in the display tank as controlled by the return pump.

The first and best method is with a display tank that is drilled, allowing water to simply drain into the sump.

Being built-in, this is the best method as it does not require an additional hanging device, and although the other method I will discuss is usually safe, this one is definitely the safest. Water passes through the drain pipe and out of the tank to the sump. Water is pumped back into the tank. Images courtesy of All Glass Aquariums, www.

Water is pumped from the sump into the display tank. As the water in the display tank rises over the top of the overflow wall the chamber behind the wall begins to fill with water.

As this chamber fills up to the opening in the drainpipe, water is fed by gravity back into the sump. As long as the amount of water pumped into the display does not exceed the capacity of the drain pipe, the water level in the sump will stop dropping, the water level in the display will stop rising and the exact amount of water that is being pushed to the display will also drain back to the sump through the drainpipe.

Likewise, the same considerations must be made with the other type of device that allows tank water to drain into the sump, an external overflow device. This is a hang-on-the-tank unit that is used on standard display aquariums that are not and cannot be drilled, due to their tempered glass construction. The external overflow box runs on the same principle as the internal overflow except that it uses siphon tubes to move the water from the display to the external overflow box, which contains the drainpipe to drain the water to the sump.

Some additional considerations must be made with these types of overflows. This should ensure that when the return pump is not operating, the tubes that siphon water from the display into the external overflow will remain full of water and will therefore begin to siphon water again as soon as the return pump starts back up.

If these tubes do not maintain their siphon, however, when the return pump resumes operation the water level in the sump will continue to fall and the level in the display will continue to increase, and most likely will overflow. Some precautions can be used such as a small powerhead with its output aimed into the siphon tube, or an air pump connected to the tube to resume the siphon. Even with these precautions, the siphon tubes may not hold their siphon or restart after the pump begins operating, which will result in a mess.

The tubes that are used to siphon the water often fill with algae and other growths, which reduce their potential drainage capacity. Therefore it is necessary to remove and clean these tubes occasionally. Finally due to the size of the external overflow box, it is difficult to build drainpipes inside them, such as the Durso and Stockman style standpipes.

These are drainpipe modifications that can be used in place of a straight drainpipe, for noise reduction. Figure 4: A typical external overflow box is shown above. The image shows the clear internal box with its surface skimming groves; the two U-tubes that siphon water from both the display and the external overflow box, which contains the bulkheads; and the pipes, which drain water to the sump.

The second component in sump design is the return pump. Many, many types of pumps are available that will work for any application, and many pumps will not work as they may be too strong or not strong enough. When purchasing a pump to use on your sump setup, you must get one that will push water the through the return plumbing the distance required to get it to the display.

Therefore you must find a pump that can push water to at least the height from the sump to the top of the display, and still move a satisfactory amount of water through that height.

Typical powerheads will not work here. You will have to get a pump that can withstand significant wear and perform constantly. With this consideration, understand that the gallons-per-hour rating applied to the pump cannot be used to determine how much water it will actually move under these circumstances. As an example, a pump rated at gallons per hour will probably produce a total flow through of only gallons per hour after the water travels through and up the return plumbing.

When using an external overflow box, you should target a minimum flow rate as well. If an external overflow box is rated at gallons per hour, a pump that moves only gallons per hour may not be enough to keep the water flowing quickly enough and constantly enough through the siphon tubes. Regarding the return pump, a few other factors can help to guide your decision. Obviously cost is an important one, and the price of usable pumps for sump applications can range from 50 to several hundred dollars.

It is possible to use internal, submersible pumps or external pumps. Each has pros and cons, including ease of setup and maintenance, space required and noise. Another consideration is power consumption, at least for those interested in conserving energy. The final component in the sump and overflow application is the sump itself. As stated at the beginning of this article, a sump is nothing more than an external container or vat that accepts drain water and, as such, for an aquarium application it can be just that simple.

A standard sized aquarium that fits in the available space under the display tank can be used with no modifications.

Many people include a couple of baffles in the sump, just before the return pump, to help diffuse air bubbles. These prevent, or at least reduce, the amount of tiny bubbles that find their way into the return pump and the display, which can be unsightly and even irritating to the tank inhabitants, as well as causing cavitations in the pump.

Baffles are simple dividers in the sump, placed just before the return pump in a configuration that makes water flow under and over them in a series. Sumps can, however, take on a whole new dimension of filtration. These filters are external, like a sump, but are protected from overflows and accidental drainings by being pressurized. Similar to a sump, you will setup the intake and return tubes from your main tank to the filter that usually sits under your tank.

Inside the canister is a variety of mechanical link and biological link filters. As with the hang-on filters, it is critical to your biological filtration that you never replace these components.

Both of these options are easy alternatives to a sump. Most commonly, a sump setup will be sold as a kit with biomedia. You can use this or a simple plain aquarium and add your own media.

Sumps are filled using gravity with a pump to return water to the tank. You will need appropriate hoses to move the water back and forth from your tank. It is recommended that you employ a skimmer box to cycle water in between your tank and sump. This will decrease the pull off the outflow to prevent animals from being sucked into the sump.

It also acts as a fail-safe to protect your sump from accidentally draining your tank. Ideally, you should set up your outflow and inflow in opposing spots so it creates a gyre in your tank. Connect tubing between overflow skimmer to sump inflow. If you are making your own sump without a kit, inflow from the tank should come into one side of the tank and return on the opposite side. Ideally, your inflow should cover the top of the tank and the outflow collects water from the bottom after it flows over the biological filter media you have chosen.

Setup your return hoses from the sump pump to return water from the sump to the tank. If you lose power, your sump will have to hold the extra water in the lines and any additional water that is pulled via gravity. Keep the return hose close to the top of your water line in your main tank. If you lose power or your pump fails, this way it will not drain your tank.

This is also why you should place air pumps above your tank. Choose a sump size and fill line to accommodate any accidents. Position the return so it flows through the tank before reaching the outflow. If your outflow is too close to the return to your sump, you are not filtering the entire volume of your tank.

This is not the same type of sump pump that keeps your basement dry! Most kits will have an appropriate size pump to match the flow of gravity from the skimmer basket and tubing size selected. If you are making your own, it is critical to match the flow of gravity to the pump return.

To gage the outflow, start your skimmer basket by priming it with water from the main tank. Catch the outflowing water in a measured container. Time 10 seconds from once the flow has established and watch and see how much water flows out.

The gallons per second will tell you exactly what type of pump to buy. If you are unable to perform this test, buy a pump with a variable speed switch to manipulate the flow to match the outflow. With the correct size pump, start the gravity outflow and plug your pump in. Watch your sump line carefully to make sure it isn't creeping up or sinking too low.