no no no!!
not "under
gravel"!
biggun said "internal under
water canister filters Eheim makes"
huge, major difference!
underGRAVEL filters are major nightmares, they sit completely under the gravel, along the entire bottom of the tank, and are amazingly dirty,
they are by far the worst type of filter to get, they result in filthy tank conditions, because you cant clean the gunk that collects under the filter plate..im amazed they are still even sold:
"The Undergravel Filtration Controversy"
http://www.athiel.com/lib/ugfilterarticle.htm
what everyone is saying you need is a
cannister filter.
they sit completely underwater, not on the tank edge, and you can easily lift them out of the tank to clean the filter media..
very efficient, clean, and easy maintance filters..
thats what you want!
here are a few photos of cannister filters:
http://www.marinedepot.com/IMD/filters_eh_pro2_canister_filters.jpg
http://www.equarium.com.au/files/store/images/viaaqua230.jpg
thats the kind you need..
Power filter:
http://www.aquaworld.ca/usrimage/cascade%20power%20filter.jpg
sits on the edge of the tank..good filters, but in your case, with only 50% of the tank filled, the big intake pipe wont reach that far.
Cannister filter:
http://www.aquaticeco.com/images/items/2227_rgb.jpg
the kind you want in this case.
sits completely underwater, not on the tank edge.
these are considered the most "serious" filters..the big-time salt-water people always use these..
again, excellent filters. The "eheim" brand is often considered the cadillac of filters, but there are plenty otghers that are just as good, and not as expensive..
undergravel filter.
http://www.aquaticeco.com/images/items/13210_rgb.jpg
pure evil, stay away at all costs.
If I ruled the world, any aquarium under 5 gallons, and undergravel filters, would be illegal..
Scot