How a Filter Works

We've all heard of different filter designs that serve various purposes. There are undergravel filters, sponge filters, power filters, internal filters, HOB filters.....but as far as I know, all of them have more or less the same three basic functions:

1. Biological Filtration: storage of beneficial bacteria necessary to maintain a proper Nitrogen Cycle.

2. Mechanical Filtration: removes physical debris (rotting plants, dust, specks of this and that)

3. Chemical Filtration: removes discoloration of water, harmful & beneficial chemicals such as medicine and heavy metals using activated carbon (black looking "rocks")

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1. HOB (Hang on Back) Filters

- This is the most commonly used filter in my experience. It hangs onto the back of your tank because there's a curved gap between the intake tubes and the filter media box. Usually on aquarium lids there's a perforated space that you snap off so you can fit your filter into a space on the backside of the aquarium.

- Price range: $20-$50

Setup and How it Works

1. Assemble the parts according to the instructions. Make sure everything fits snugly. Check that you have all the pieces. Rinse filter cartridges to get rid of carbon dust (black dust)

2. Plug it in, make sure there's a drip loop so trickling water won't damage your electrical sockets and the machinery. (If your model needs priming, pour water over the top of the box to get it the pump started and the water flowing. Other models should be self-starting)

3. Check that water is flowing at the correct rate and is constant. Adjust flow rate (if possible) with the adjusting valve. You turn it right or left to increase/decrease water flow. It's usually found at the top of the intake tube where it empties into the box.


Basically, the motor will spin a rotating object called the impeller, forcing water up the intake tube. It empties straight into the "box" containing the filter media, water runs through the filter media (which traps debris, eats up waste, removes chemicals etc.), and comes out clean the other end.


2. Air Powered/ Sponge Filter

- Simple design powered by an air pump on the outside of the tank.
- Usually used for fry tanks or hospital tanks because it produces very little current
- Low filtering capacity, can't handle too many fish.
- Extremely cheap and a common DIY (Do-It-Yourself) Project!! (Price: $10-$15)

How it Works

- A plastic box containing filter media (a sponge or something similar) is suctioned onto the tank in a corner. It connects to air tubing that leads to the air pump outside. The air pump pushes air into the water, forcing the tank water to move into and through the box, which will filter the water and then spit it back out again -clean....ish.



3. Internal Filters

- Works in the same way as the HOB filter except internal filters, well, fit INSIDE your tank.
- Small size, compact; thus designed for small tanks (MAX 10G I'd say). (Some fit into your palm)
- Quiet (depending on brand) with a steady current
- Poor filtration capacity, doesn't cycle a lot of water and clogs easily.
- Requires frequent cleaning. If it only has one filter cartridge, your tank will often be sent into a mini-Nitrogen Cycle all over again because you're removing a lot, (if not all O_O) the bacteria!!

- Price range: $20-$30


4. Undergravel Filters

- Cheap, simple design, quite effective IF you maintain it properly
- Great filtration tool if properly used.
- Difficult to clean THOROUGHLY; requires constant maintenance.
- Bad idea if you want to grow plants - the roots will get very tangled with the grate.
- Gravel gets dirty real quick. Lots of debris gets trapped in the gravel using this method.
- If you fail to clean gravel thoroughly, it may "get stuck" or clumped so oxygen won't aerate it properly and bacteria will die this way.


-Price range: $20

How it Works

- A plastic grate with slits or holes in it is fitted at the bottom of the tank.
- Gravel covers over this grate.
- The grate is connected to a tube that goes up to the top of the tank.
- A powerhead motor at the top will suck up dirty water from beneath and within the gravel. It will oxygenate the water, and push this water full of oxygen back into the gravel, where all the beneficial bacteria are housed.
-An attached bag of activated carbon near the powerhead can add chemical filtration.***(This method is not ideal since the carbon will get used up really fast and you'll need to replace it like every week)

-An air stone powered by an air pump can also push water up using its little bubbles.

- Gravel becomes main biological AND mechanical filtration house.
- As long as oxygen goes into the gravel, bacteria can eat waste and clean water.



5. Canister Filters

- Extremely expensive
- Very high filtration capacity for large tanks (50 gallons +)
- Very good quality filters (hence the price!!)
- Minimal maintenance required (once every few months)
- Requires a lot of space (probably a cabinet stand) to store because they can be big.
- Looks cyclindrical in shape
- Can by noisy or super quiet depending on brand.


Price range: $100- $400


How it Works (as far as I understand....it's pretty complicated)

1. One tube draws dirty water from aquarium into one side of the filter. It goes down and through the filter media (bio/mech/chem filtration) and out the other tube as clean water into the tank again through a spray bar (diffuse spraying = less disturbance)

2. Powered by a heavy duty water pump, built into system or external.

3. Locked lids and sealed container = no spills!

4. Your choice of filter media - countless varieties to choose from!