09-07-2011, 09:30 AM
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HOB (Hang on Back): These are power filter versions of the old bubble up filters that hang on the back of the aquarium. They typically use magnetic induction motors to drive impellers to pull water into the filter chamber, then return water to the tank in a water fall like flow. Many use filter cartridges while others have a chamber to accept mechanical, chemical, and/or bio-filtration media.
Box filter: another type of bubble-up filter that sits on the bottom of the tank and contains floss and activated carbon. These are somewhat unsightly and aren't used much these days.
Sponge filter: The sponge filter is a simple open pore sponge and an air pump typically pulls water through the sponge which traps very small particles and serves as a 'platform' for bacteria colonies. Some sponge filters have been modified to accept power heads for greater water flow.
Canister Filter: Canister filters install below the tank, using a siphon action to pull water from the tank and a motor driven impeller for the return flow. Most use sponge material for initial filtration, then have two or more baskets/chambers for additional filtration media. Most will come with activated carbon as well as some type of bio-ceramic media. Canister filters are typically only used in larger aquariums, sometimes in conjunction with one or more HOB's.
UGF (Undergravel filter): The UGF is perhaps one of the oldest air driven filtration devices. It's a plastic plate with slotted holes that sits below the gravel substrate and typically uses air to pull water up through tubes on both back sides of the aquarium. The UGF mimics how nature filters water and is an excellent mechanical/biological filter. There has been great controversy over UGF filters. Detractors felt that the air driven bubble up does not move enough water evenly from across the gravel bed. Designers added power heads to move more water. Detractors felt the bed plugged with Detritus too quickly so reverse flow UGF's came along. The 'problem' with conventional UGF's is like ALL filters, the filtering media needs to be periodically cleaned. In this case the gravel. If not done, the gravel actually plugs with decomposing detritus and becomes an evil 'nitrate factory'.
If/when the gravel is routinely siphoned to remove particulates, the UGF is perhaps one of the simplest and most economical filters there is. Note that the reverse flow UGF resolves this at the cost of a conversion and a couple of power heads (making it a much more expensive filter).
Note: Many tanks are set-up with multiple filters, sometimes more than just one filter type. I have a 10g with a UGF and a small HOB. My 60g has two HOB's. A large tank may have a UGF, or canister and one or more HOB's. A large heavily planted tank may just have a small sponge filter. The amount of filtration is what's necessary to keep the water clean and clear. HOWEVER, the very best 'filtration' is the 25%-50% weekly water change (WWC) that removes polluted water and replaces/refreshes with fresh, clean water - much like nature refreshes fresh water with rain.
Last edited by AbbeysDad; 09-07-2011 at 09:33 AM..