Built-in Corner Overflows

[trace_lynn]

Just wondering when exactly you would want an overflow versus just using a canister and/or wet/dry filtration?

[AquariumPro]

Hi Tracy and welcome to the boards.

A little confusion exists here, so I have to provide a little background. There are three types of filtration: Biological, Chemical and Mechanical. We discuss and describe these in detail in our articles (http://www.aquariumpros.com/articles/) so I won't do that here. Your question indicates that you may be unclear on what these types of filtration do and what types of filters are suitable for each type of filtration so you may want to read the articles we have on filtration.

What you are concerned with here are the mechanical methods used to connect filters to your tank. Within the three types of filtration, filters take two forms: Closed systems and open systems. Examples of closed systems are canister filters and fuidized-bed filters, that are sealed and operate under pressure. Other types of closed systems include filters that are self-contained and operate under water such as internal box filters and undergravel filters. All closed systems have one thing in common: They do not have components that are directly exposed to air.

Examples of open systems include wet-dry filters and Berlin sump (or reservoir) filters. These types of filters are open to the atmosphere and usually take the form of an open box of some sort. They always have one major thing in common, and that is they sit below or hang on the back of the tank, and are fed with water that is drawn from the surface of the aquarium. If these filters were connected to an intake that drew water from below the surface of the aquarium (like a canister filter intake), they would flood your floor, and that's where the overflow comes in.

These types of filters require an overflow, also called an overflow prefilter, which draws water from the surface of the aquarium and delivers it to the filter via gravity. There are two types of overflows: Built-In and Hang-On. The Built-In overflow is inside the tank and simply allows water to overflow into it where it drains down into the wet-dry or Berlin filter. The Hang-On overflow is more complicated. It draws water from the surface into an overflow inside the tank (called a "waterfall" cup), then a siphon tube is used to take that water and pull it over the top rim of the tank into a box that hangs on the back of the aquarium where the water then drains down into the filter below the tank.

Hang-On overflows should only be used if you have an existing aquarium to which you want to attach a wet-dry or Berlin filter. They are more problematic than Built-In overflows and more difficult to set up, so if you are buying a new aquarium and wish to use a wet-dry filter or set up a reef tank and use a Berlin system, you definitely want to get your new tank with a built-in overflow.

Wet-dry filters are usually used only for marine aquariums, but they work quite well for freshwater too.

Below is a drawing of a typical wet-dry filter set up showing a built-in overflow.

http://www.aquariumpros.com/images/forums/typical.jpg

Hope this helped!

[trace_lynn]

Thanks for the reply, that helps out.

I have freshwater aquariums and I am currently looking for a 75 gallon long (60"), but was given the option of a over-flow and didn't understand exactly what its purpose was. I will read the articles next - but I believe I just misunderstood the "wet/dry" concept. When I think/say wet/dry - I am thinking of a HOB Biowheel type power filter which is what I currently use (Penguin Biowheel 330) and an overflow works with a "TRUE" wet/dry which is not what I am wanting because I am looking at a planted aquaria also and that would end up with a lot of lost CO2. I'll stick with my choice of an Eheim canister filter.

Thanks so much for the quick reply and article info.