The biological filter, also called the "undergravel filter." The undergravel filter uses bacteria in the gravel to purify the water. Two types of bacteria exist in the gravel layer. The first feed on ammonia, which is what fish "waste" mostly is. The bacteria "convert" ammonia into nitrite. The second type of bacteria feed on these nitrites and convert them into nitrates, which is harmless to the fish. This type of filter never wears out, never needs a cartridge changed, and requires only a 25 percent water change of the tank twice a year. This also keeps the fish healthier because major water changes tend to "shock" the fish and make them vulnerable to disease.

Power filters are the best way to go. Unlike Undergravel filters, you can actually clean them. Over time, undergravel filters build up a sludge beneath the filter plates that begin to leach nitrates into the water and cause overall water quality to go down. While these filters work from a biological standpoint, they do not do any physical cleaning, and in fact, contribute to the mess. In order to clean them you must dissassemble the entire tank. Power filters, either the hanging kind or the canister kind are very effective and easy to maintain. They keep the aquarium cleaner, and are quiet to run. Water changes should be done often and regularly, every week or two is best. That advice of twice per year is terrible. Fish do not go into shock from water changes, and get more diseases from dirty old water then they ever can with a water change. The trick is to keep the temperature the same.

A bio-wheel filter is the best circulating filter out there. It filters out the particles in the water such as food or solid wast that was not broken down by the live filter. Also a bio-wheel has bacteria that grow on the surface of the filter cartridge that enters the tank as well as biologically filters the water that passes through it.

For all tanks, the hang on back power filters are honestly the best filtration you can get for your money. Be sure to get one with either a biological filter sponge, plate, or wheel. I recommend one that allows a sponge or plate over one with a wheel, simply because the wheel filters tend to be more expensive to maintain. For excellent filtration, have filters rated for about twice the volume of your tank, for example if it says adequate for a 20 gallon tank, then it's perfect for a 10 gallon. Never use a UGF (under gravel filter) or reverse UGF with an airstone, the flow is simply not powerful enough. You must purchase powerheads for this kind of filter. However UGFs are really crappy filters, because they tend to clog easily, and are frankly more of a messy pain in the butt than they are worth. You can get much better bio filtration with a trickle (aka wet/dry) or fluidized bed filter. Cannister filters are good for larger tanks where you would basically need six hang on the back filters just to get enough water flow. The downside is these are expensive, a pain to maintain, and well, again, expensive. Lastly, sponge (in tank) filters are good for some biofiltration, but really only good for fry tanks. So to answer your question - I'd say either get one of the Penguin Biowheel filters or a Haagen Aquaclear for a tank 55 gallons or under. If you're running saltwater I'd get a protein skimmer going as well.

Everyone is going to have a different answer for this question, but honestly I believe it depends what kind of aquarium you are looking to set up. For a freshwater aquarium? I'd say the highest quality filter would be the canister filter, the next step down would be a hang on the back filter. Canister filters allow your water to be pushed through several different filtration medias allowing biological and mechanical filtrartion. Hang on the back filers have only a couple of medias to flow through, and tend to get clogged up very easily (but they will do the job if cleaned correctly.) For a saltwater tank? Well, there are tons of different options, but what you absolutly need is a protein skimmer and (generally, in my opinion) a whole lot of live rock. But there are so many ways to set up a saltwater system that you should look into how much money you want to put into it, and then decide.

Every aquarium needs different filters. hang on back bio wheels are popular. I love my canister filter.

Hello; The best filter for any aquarium is one that traps waste and converts the waste into harmless compounds. The filter must have a large filter area and have a good flow of water through it --- 1 to 3 times the tank volume per hour. The underground filter is the only filter that meets all these requirements. The UGF has a filter area of the entire floor of the tank and the thickness of the substrate. It traps waste and converts it into harmless compounds. With a good thin air stone that creates small bubbles it easily moves the required amount water. It is not messy and can easily be cleaned with a simple siphon device that should be used on all substrate regardless of the filter type. If more flow is required many different flow rate powerheads are available. A filter must pass water through all the filter material to be effective. The faster the water flow through the filter given a certain filter area and a maximum conversion factor, the less nitrogen conversion takes place per pass. A filter must trap and convert waste to Ammonia then Ammonia to Nitrite then the Nitrite to Nitrate. People who do not understand this say the UGF produces to much Nitrate. Well, this is it's job --- and it does it well. If the substrate is cleaned often is has very little to convert and the Nitrates drop. What could be easier than siphoning the substrate and adding new water? This removes waste and dirty water high in dissolved organic compounds. I have used and do use most of the filters mentioned along with my UGF's. I even use a UGF on the left side of my Reef Tank under 2-inches of aragonite gravel. I use other filters for chemical (carbon) filtration. I recommend you evaluate the different filters and chose your favorite. Enjoy! OFM

I have a UGF filter with 2 uplift tubes, I also have another tube I rigged myself to a hang on filter which removes the waste that is collected under the gravel. The good bacteria is on the gravel, which is very good for the tank, but the hang on filter eliminates all the harmful bacteria in the bottom. As far as water changes, all aquariums need it. Salt water more than freshwater, and the more fish you have in your tank, the more frequent you need to do a water change. And always test your water at least weekly for amonia, PH, nitrates, and nitrites. Also, all gravel and substrates need regular vaccuming too. I do know that anyone that says UGF filtration is bad, definitely does not know anything about the BIO process of aquariums.

I have undergravel filters on all 6 of my aquariums and have the hang on filters hooked into the undergravel filters with one bubbler with charcoal filter in the middle of the bottom filter..One 50 gallon tank stays cloudy no matter what I seem to do.. The others are OK, the discus tank stays light yellow with the peat in the planter.I change about 1/3 of the water every week. Any suggestions? I am pretty new at this many fish

It depends on the fish type, and density. For a tank with a lower population, and without gravel digging fish, I prefer a UG filter with a power-head. Weekly maintenance simply involves using a siphon vacuum gravel cleaner when doing a water change. For a more populated tank, or "messy" fish, I think the best value is a bio-wheel.