07-26-2011, 09:58 AM
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From my research on bacteria, it seems that sponge filters, canister filters and wet/dry filters will all provide roughly equal biological filtration provided they are properly maintained. The wet/dry work for very large tanks, but no better than canisters on tanks under 200g.
At this point, one must also consider the intented aquascape, as AbbeysDad mentioned. Planted aquaria do not require biological filtration because the plants are doing that, so any filter that encourages this would be detrimental. A sponge filter on tanks up to 55g and a canister over that work well. Both of these also have minimal flow, or in the case of canisters the flow can be adjusted; and this is imortant for plants and also fish, since most planted tanks will contain forest fish and these do not appreciate a lot of current, with a few exceptions.