Wet/Dry and Sump Filtration

What is a WET/DRY filter

A Wet/Dry filter is usually identified by having separate compartments with the main compartment being filled with "Bio-Balls". These balls are often blue in color and are spherical in shape yet have lots of small "fingers" coming out from the middle. These balls are usually suspended above the water that is in the sump portion of the tank and the water coming from the tank's overflow trickles over the bio-balls. This is where the WET/DRY filter gets its name. Since some of the bio-balls are wet and other balls are dry. Having the water trickle over these "fingers" provides an oxygen rich environment for the ammonia and nitrite consuming bacteria a location the flourish.

This oxygen rich environment is the main reason this type of filter is less desirable for a reef setup than it is for a fish only setup. The byproduct of the ammonia/nitrite cycle is nitrate. Fish are less sensitive to nitrate than corals and some other inverts. Nitrates have been known to climb to levels well above 50ppm on established tanks with a wet/dry filter. Some hobbiest have had success in keeping nitrates down by also implementing a DSB or having an abundance of live rock to help remove the nitrate.

What is a Sump

A sump is a location that extra water is located. All wet/dry filters also have sumps but you can have a sump with out having a wet/dry. If you remove the bio-balls from your wet/dry filter you now have a sump.   Most people put equipment like a protein skimmer or heaters in the sump. This hides them from view in the main tank with out having to go with out them. A sump also provides room to place activated carbon bags if the hobbiest needs to filter with carbon or any other form of chemical filtration.

What do I need to have a wet/dry or sump

An overflow
Hose or PVC pipe
A decent sized container (when the sump is in operation you want it to be filled only to 1/2 capacity so size appropriately)
return pump

What keeps the system from spilling water all over?

This is a question I see a lot on reef forums. So I decided that there might be a need for such a resource. I hope the description below helps answer any questions you should have about the entire process

How does it all go together

It all starts at the overflow. Some larger tanks are sold with overflows built in. These are often sold as "reef ready". If you are lucky to have one of these thanks than congradualtions as you don't have to worry about buying an overflow since it is build in. If you do not have a built in overflow then your going to have to either make your own (not recommended if you have not worked with acrylic before) or purchase one. When buying an overflow make sure you size it to handle the flow rate your pump is going to be filling the tank at.(more on this later) The overflow is such a key to the sump or wet/dry filters success its crucial to not skimp and get a cheap or smaller overflow than what you really need. If the overflow is to small then the pump in the sump is going to be filling the tank faster than the overflow can drain the water thus you have a flood. If the overflow is poorly made and clogs up you will have the same flood as a result. Also make sure you use a good hose clamp or PVC glue on the connector going from the overflow to the sump. If this hose should come loose the net result once again will be a flood.

Hang on overflows require a siphon to get the water from the tank up and over the side of the tank and then down into the back portion of the unit. This is achieved with the help of a "U" or "J" tube. This is because of the shape. The tank side of the overflow has "fingers" that strain the water (very coarse items only), these fingers also are adjustable so you can set the water level you want the tank to maintain. Once the siphon is created the water will be pulled up and over the side of the tank via the "U/J" tube. If the water level is above the two ends of this tube then the siphon will start back up should a power outage occur. If air gets in this tube then you will have to start the siphon back up with the help of some airline tubing.

You then plumb the overflow to your sump. Once the water is in the sump is can be run thru a protein skimmer or warmed up with a heater. A return pump will then need to be plumbed it back up to your tank. If you don't have a spair tank or a converted wet/dry filter then you can make your own sump. One of the cheapest sumps is a plastic tub of some sort. Remember when sizing your pump to account for the effect of gravity on the water as it pumps up. Measure the height that the pump has to push the water. This is your "Head Height". Find a pump that pushes the amount of water you want to circulate at the correct head height. In theory the pump is consistently trying to overflow the tank while the overflow is trying to drain the tank so assuming your overflow can handle equal to greater capacity than the pump can pump you will have equilibrium.

A sump is good for multiple reasons.

1. The sump adds water capacity to your system. We all know the more water in your system the more stable the water quality. (As a general rule)
2. Provides a place to put unsightly equipment like skimmers and heaters.
3. Allows for easer water changes. If you size your sump to a point where when its active the actual amount of water you have in your sump is equal to the size of your normal water changes then you just empty your sump and then put water back in the sump to your water line and "POOF" water change is complete. (You will have to shut off the pumps in the sump prior to this)
4. Easy way to keep your tanks water level full all the time. As water evaporates the water level in the sump goes down not the water level in your tank. Then just add replacement water to your sump and thus less chance that your tank critters will realize that freshwater was just added to the system.

I hope this helps explain how a wet/dry or a sump works and how to set one up. Should you have any questions about this page please either e-mail me or leave your comment in my guest book.