Why an Overflow box?

[Haskellf]

Why is an overflow box listed as " is the most efficient method of draining aquarium water to a filter." Is it really necessary to have one if you already have a power filtration and a skimmer? I don't understand the need for it if you already have an Eheim Professional 2 series filter, for example?

BTW- For a newbie, thanks for everyone's responses, they've been very helpful

 

[Anonymous]

The quote if from the marketing department...

Anyway, protein film sometimes get accumulated on the surface of the water, and physical skimmer (not protein skimmer) or surface agitation is need to break up the film. An overflow box is one such device that can be helpful in the task.

 

[Len]

An overflow box is only necessary if you plan on using a sump. Sumps can hold big skimmers and oodles of other equipment like calcium reactors, heaters, chemical filtration, etc. On smaller tanks, a sump is not necessary, but larger tanks will invariably need one if not just to house a large skimmer and big circulation pumps.

Canister and hang-on powerfilters don't need overflow boxes. They're "complete" filtration systems, although they are really better suited for freshwater and fish-only marine aquariums then they are for reef tanks.