Powerheads

[sic0198]

What do these do? Do I need one?

 

[geo7x]

powerheads are basically something that sucks in water one end and shoots it out the other, it gives water circulation.
They are mainly used for SW aquariums that have live rock as its 'filter', this is porous and therefore nitrifying bacteria can live in it, and the powerhead is there to create water circualation around the tank and therefore a water flow through the porous live rock.

In the standard FW tropical aquarium you dont need on of these unless it is part of a filter, particularly undergravel, or if you want it for any other reason.

 

[TerraDreamer]

I'm old school; I still use an undergravel filter, as well as an HOB power filter for free-floating debris and the additional provided biology. I only use one powerhead on the UG filter, and use an airstone on the other tube. This has always provided excellent filtration results for me. Be aware that a powerhead creates substantial current within a tank and many species don't like that. I wouldn't opt for a powerhead on anything less than 29 U.S. gallons, and that powerhead should have an adjustable flow rate.