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Generally, how do filters work in an aquarium?

Aquarium Filter Basics

Marc Grover (Professional Aquarist) gives expert video advice on: Generally, how do filters work in an aquarium?; What are the best filters for a small freshwater aquarium?; What are the best filters for a large aquarium? and more...

Generally, how do filters work in an aquarium?

When you're talking about filtration in an aquarium there are three basic types in any type of system. There's biological, chemical, and mechanical. Biological literally grow and house aerobic oxygen-using bacteria which convert, by basically eating ammonia and nitrite, and the by-product or the waste product ends up being nitrate which is not very toxic. That's your basic biological system. It is aerobic bacteria needs good rich oxygenated water to go through, either your gravel bed or your wet-dry triple filter where they live. Chemical filtration is typically either a hang-on filter, that hangs-on at the back of the tank. A section in the wet-dry that houses carbon or some kind of mechanical absorption resin that specifically targets uric acids, copper, other heavy metals that while not deadly to a fish but most of the time can cause some concerns or some issues for them. And the last thing is really what I call the people filter. It's the physical-mechanical part of the filtration system. You're using a type of padding, or a type of floss or cotton to physically pull out particulates, whether its pieces of plant or excess food, anything in the water that will be a particle you could actually see with your naked eye. Those particles will tend to make the water look not as clear as it should. And if you got a good mechanical filter, it'll literary extract those components out and make your tank crystal clear.

What are the best filters for a small freshwater aquarium?

When you're doing a small tropical freshwater aquarium, you want to start with the biological filtration. The number one method for me, in my opinion, is to use an under gravel filter and there are ways to make that function whether you are using a power head or an air pump. Then, you can get away with just that although you're tank typically isn't as clear as you might like it to be. You can then augment that filtration with either a hang on the back or a canister filter that sits underneath the aquarium, and that will accomplish both the mechanical water polishing filtration and it will take some other toxins out with chemical filtration, namely carbon or other absorption resonates. A lot of times people will try and cut corners and buy a prefabricated kit. Most of the time it is totally skipping or really downplaying the biological aspect of the filtration and focusing on the make the water clear for the viewer filtration. While that's a great sales point, it doesn't work in the long term for your fish because it really ignores the eco system basis of keeping your fish alive which is the biological aspect of the filtration system.

What are the best filters for a large aquarium?

When you get into a larger system, specifically a tropical freshwater, what I like to do is instantly work in flexibility. The type of filtration that you can use on a large saltwater system also works really well for a large freshwater system. Typically what will happen is that if you do have a large freshwater, there is a decent chance that you are going to want to shift to saltwater someday. And I'm thinking ahead of the game saying "well why would you have to buy everything all over again" to accomplish that. So what I'm going to do is take the tank, have it ordered with an overflow prefilter box built into it, and then go to the wet-dry system that I would also recommend for a saltwater tank. It's a biological system, again the heart of every system, and it's really efficient so you can use that for any type of system and especially works really, really well on bigger systems, whether it's a freshwater or saltwater.

What is an 'under gravel filter' for an aquarium?

An under-gravel filter is pretty much exactly what the name implies. It's a filter that goes underneath the gravel in the aquarium. It's not a filter like you're thinking of, that water comes in and water gets pumped back out. It's a plate that sits underneath the gravel that houses nitrifying microscopic bacteria. Those bacteria convert toxic wastes, ammonia and nitrite, into nitrate which is not toxic or has a low toxicity to it. It's a biological filter. Biological filtration is a heart of every system. It is different than a mechanical filter, that is a pump that's pulling water out and cleaning it, then pushing it back in. An under-gravel filter is best used, or is most commonly used, in freshwater application and not with live plants because live plants will shoot their roots down and sometimes that'll kind of compromise the function of the under-gravel. It doesn't mean you can't use it for other systems, i.e. saltwater, it's just not super efficient and you can get away with not super efficient in freshwater. It's also one of the least expensive, biological filters you can get compared to the ones with saltwater; so that's why the trade off is less efficient, less cost, and that works better in freshwater.

What is a 'hang-on mechanical filter' for an aquarium?

A hang on filter or a water fall filter is again, as the name implies, it usually hangs on the back of the tank. It has an uplift tube that drops down into the water and an impeller that is inside the filter mechanism that creates a suction. Water gets pulled or sucked up the uplift tube, and then pushed through the various stages of filtration media, in that hang on section, the compartment and then water falls back into the tank. So 1, 2 going up, water fall coming back out. And typically, the filtration stages are a carbon pack, and a sponge, and maybe another type of chemical resin that tries to eliminate ammonia, or what have you. And sometimes they work and sometimes they do not. That is basically what it is.

What is a 'BIO-wheel' for an aquarium?

A BIO-wheel is a modern version of a biological filter. It works like a wet dry but it's really compact. It's a small wheel that has a lot of pleats in it, and it's typically on one of the hang on waterfall filters. The water gets sucked up through the tube and goes to the filter stages, and then as the water is falling back out of the tank it strikes this BIO-wheel. The BIO-wheel is not totally submerged. It's spinning through the waterfall. If you can imagine a barrel with fins on it spinning in a waterfall, part of the time it's submerged but most of the time it's in the air. It's a wet dry filter, and bacteria need oxygen so all that air is hitting all the bacteria and it's working like a under gravel. It doesn't have the surface area that an under gravel does, so it's not quite as efficient, but it is a combination filter where you have got the water for mechanical aspect and the BIO-wheel biological aspect.

What is a 'canister filter' for an aquarium?

A canister filter is literally a pressurized canister with an in tube and an out tube. Typically, they're located below the tank and the tubes come up the back. Again, water is drawn via suction into this canister. It's got a motor that drives a propeller that pulls the water into the canister. Forces, it's pressurized, forces it through these different stages of filter media. Again, like a hang-on filter, just much more massive surface area. So you can put a lot more carbon, a lot bigger sponge, a lot bigger mechanical pre-filter mechanisms in there. And the canister filters are kind of the big brother of the hang-on filter. They're bigger. They're badder. They're bolder. The just do more and they are more efficient and more expensive. They typically don't leak as much either and they are stealthy. You can hid them underneath your tank. You've only got small tubes going in and out of your tank as opposed to this contraption or apparatus hanging off the bank of your tank.

What is a 'wet or dry trickle filter' for an aquarium?

A wet/dry filter, it's kind of as it's name implies, but it's basically a box, and part of the box, half of the box, has got a bunch of computer designed what they call "bio balls". And they are biologically designed to hold a lot of bacteria. And basically water will overflow or drain out of your tank through a tube and drop over a drip tray, which is a tray with a bunch of holes in it. And then trickle, or rain, over these bio balls. 80% of the bio balls will not be submerged at all; they'll just have this trickling effect of rain going over them. The bottom couple of inches will be submerged, of this whole box will be, especially the half with the bio balls in it, and then the water will be pumped back out either through a pump that's submerged in the other side of the filter, the open end of the box, or through an external filter that's plumbed into that open end. Wet/dry's are right now, in my opinion, the most efficient, or one of the most efficient biological filters and, again, my credo is biological filtration is at the heart of every system. And if you can have an efficient one, all the better. They are also almost maintenance free. So they work super, super well on any type of system, but they really fly and shine in a salt-water tank. I wouldn't recommend lesser filtrations for a salt-water tank, but I would recommend this filtration for a fresh-water tank. It's the king of kings; it can do all of it.