Overflows and Drilled Tanks

[swnewbie]

I am a first timer here is SW land. I have a couple of basic questions that may have been asked before, but I must be such a newbie that I can't see the answers anywhere.
I have some experience with fresh water, many years ago. However, I am now interested in getting into SW, and am reading what I can find. That's how I found this site.
One thing I have read, concerning tanks that are manufactured these days, is the concept of overflows and drilled tanks. I have no idea what these terms mean. It appears some tanks come with pre-installed overflows and drilled holes, where others have them installed/drilled after the tank is built. One description, of an overflow I found sounded like a bio-wheel filter my LFS carries (sucks up and filters water?). I have read that bio-wheels are not that good, so that confused me even more.
So, my questions are....exactly what are overflows, and why are some tanks drilled? What purpose do they serve. If a tank is advertised as having an overflow, will it automatically be drilled? Conversely, if a tank is drilled, does that mean it has an overflow.
Thank you.

 

[sjt1107]

Most "reef ready" tanks come with a built in overflow. A section of the tank, usually a 5in X 5in area (depending on the tank size) has been built into the tank with louvers at the top for the water to "over" flow into and down to the bottom of the overflow area where a hose connects it to the sump which usually includes a wet/dry filtration and protein skimmer. A pump then pumps this filtered water back through a hose up the overflow and back into the tank.
Acrylic tanks can be drilled professionally or by the home aquarist. But, glass tanks can usually only be done propperly by someone with experience in drilling glass.
If a reef ready tank is not what your looking for, they make filters, protein skimmers, etc...that all hang on the side of the tank, too.
Good luck and welcome to the board! :cheer: :cheer:

 

[thomas712]

Originally posted by SWNewbie
So, my questions are....exactly what are overflows, and why are some tanks drilled? What purpose do they serve. If a tank is advertised as having an overflow, will it automatically be drilled? Conversely, if a tank is drilled, does that mean it has an overflow.
Thank you.
An overflow box is a box inside the aquarium that water flows over the top of and down to a drain where it flows to a sump or wet/dry filter. The top of the box has slits in it which the water flows through, so as the water pump in the wet/dry pumps water back into the aquarium, the water level rises and begins to fall through the slits. An equilibrium is reached such that the amount of water being pumped into the tank equals the amount of water that rises and falls into the overflow. Because the water must fall in through the top of the box, in the event that the water pump fails, the water level in the aquarium will only be able to drop to the bottom of the slits at the top of the overflow. Thus the tank won't be drained of its contents, and your floor won't get flooded! Skimming water at the water's surface also prevents a protein film from developing, resulting in better gas exchange at the air/water interface.
There is actually a second type of overflow box that hangs on the back of the aquarium. It siphons water from a surface skimmer box inside the tank to another box with a drain that hangs outside the tank. The biggest advantage that an internal overflow box has is that it merely relies upon gravity to work. Hang-on overflows rely upon a siphon, which can be lost frequently, to work. Because a deeper water column can be established in an internal overflow (creating more water pressure at the bulkhead), higher flow rates can be accomplished. Many people with hang-on overflows have trouble with the overflow keeping up with the water pump and end up having to restrict the water pump or buying another overflow. Cost is another advantage. You'd have to buy a REALLY big internal overflow for it to cost as much as one of the hang-on types. Internal overflows also have more space to function as a pre-filter. A sponge should be used to filter the water before it drains to the wet/dry so that debris doesn't accumulate there.
It is very convienent to have the tank drilled for the internal overflow, this will keep the water in the main tank in case something happens like the power outage mentioned above, and like was stated the drain pipe and return tube are both located inside the overflow box. So if a tank is drilled then it should mean that it does have an overflow box.
Hope that answers your questions
Thomas