Fish Tank Filter Guide

In Aquarium Filtersby PaulK


Fish tank filters are used in aquariums to filter out the harmful chemicals that form in the fish tank water. There are three main types of filtration. Biological filters, that filter out the harmful ammonia and nitrates from fish waste. Chemical filters that filter out harmful chemicals like chlorine and metals, and Mechanical filters that filter out solid particles, like excess food and other particles.

In most filter systems, there are three different filters that perform different functions.

Biological filters consist of what’s called a media that’s designed to grow bacteria consuming the harmful ammonia and nitrites from the fish waste. You’ll see many different types of filters like lava rock, bio balls, bio wheels and sponges used for this purpose.

Mechanical filters are designed to filter out solid particles in the water, so your fish tank will be nice and clear. There are many varieties of mechanical filters used.

Chemical filters filter out other harmful chemicals like chlorine and metals from tap water. Typically, these are going to be carbon filters.

The Nitrogen Cycle and Why It’s Important

When you feed fish and they consume the food, that is introducing nitrogen into the aquarium. Your fish will produce waste from the food that form ammonia and nitrites in the water they swim in. Ammonia and nitrites are not good for the fish and they will eventually die if there is too much. It would be like us swimming around our toilet water.

There are two different types of bacteria that we want to form in the filter media to eat the ammonia and nitrites and get it out of the water the fish swim in.

The first type is Nitrosomonas bacteria that absorb the ammonia and produce nitrites. The second type is Nitrobacter bacteria that absorb the nitrites and turn that into nitrates which are not as harmful to fish. Live plants help to absorb the nitrates in the water. Water changes help with nitrate level as well.

Types of Aquarium Filters Systems

AquaClear 50 Power Filter - 110 V, UL Listed (Includes AquaClear 50 Carbon, AquaClear 50 Foam & AquaClear 50 BioMax

AquaClear 50 Power Filter. Click photo for pricing info.

Hang on the back/Power filters – HOB filters aka power filters, hang on the back of your fish tank. A long tube goes in the water. A motor with an impeller sucks the water up the tube and through the filtering system in the back. The water is then returned back to the tank via a water spout. This creates a waterfall effect and doubles as aeration for the tank.

Pros: Easy to set up and maintain. Great at mechanical filtration for water clarity.

Cons: Poor water circulation because of the proximity of intake tube and return spout. Can get noisy from worn motor/impeller or water splashing back into the tank.

MarineLand Magniflow Canister Filter for Aquariums, Easy Maintenance

MarineLand Magniflow. Click photo for pricing info.

Canister Filters – The canister houses the filters and is located somewhere outside the tank. An intake tube sucks the water into the canister filters and water is returned through a tube back into the tank. You position the intake and return tube on opposite sides of the tank for maximum water flow.

Pros: Provides good water circulation. Efficient to use.

Cons: Harder to clean and maintain. More expensive.

Undergravel Filter – These filters are installed at the bottom of the tank before the substrate is put in. Water is sucked through the gravel substrate which acts as a filter, then water is returned to the tank via plastic tubes. The beneficial bacteria builds up on the gravel substrate. These type of filters are old school and not used much anymore, but are effective biological filters.

Pros: Great biological filters

Cons: Lots of substrate cleaning; needs another filtration system for mechanical and chemical; not good for sand substrate or lots of decorations.

Corner Filters – These fit into the corner of the tank and are fully submerged. They are good for smaller tanks and beginners.

Aquaneat Aquarium Bio Sponge Filter 20 Gal Breeding Fry Betta Shrimp Fish Tank (Single)

Aquaneat Bio Sponge Filter. Click photo for pricing info.

Sponge Filters – These are also fully submerged in the tank. A tube comes out of the top of a  cylindrical sponge that acts as the filter. Water is sucked through the sponge and up the tube, so you need an air pump to operate it. Typically sponge filters are for biological filtering, but you can get different grades and stack them for mechanical filtering too.  The sponges must be rinsed and cleaned every month or so.

Pros: Great for biological filtering. Inexpensive. Easy, squeezy maintenance. No moving parts.

Cons: Ugly and hard to hide because of their size. Can be noisy due to air pump and bubbling water.

Sumps: These are large plastic boxes with compartments located outside the tank. The same principle as a canister filter, but many are homemade. These are for larger tanks 75 gallons or more.

Which kind should I get?

All of the types of filter systems will work just fine if you maintain and clean them. The main thing is you want the right size filtration system for your size tank. Maybe two systems for larger tanks over 50 gallons. Preferably you want a filtration system where you have all three filters and you can swap out the mechanical and chemical filters, but keep the biological filter with all the beneficial bacteria.

The most important factors are:

  1. How many gallons per hour your system will filter. A good filter will turn over your tank water at least 8 times per hour. So on a 25-gallon tank, that’s 200 gallons per hour. Make sure your filter system is powerful enough to handle it. It should say on the box what the GPH or gallons per hour are and what size tank the filter is designed for.
  2. The type of filters you use for both biological and mechanical filtration. Use a good media like a sponge, lava rock, bio balls, or bio rings for biological filters. Use a filter pad or floss material for mechanical filters.

What are the best filters?

It’s getting harder these days to find reliable aquarium equipment. If you stick with the better brands you won’t have as many problems. Every piece of equipment you buy for an aquarium will break down at some point, so it’s preferred that you go with a company that has a good warranty, good customer service and stands behind their products.

HOB/Power Filters:

Aqua Clear Power Filter – These filter systems have a lifetime warranty. Quiet for HOB filter. They have a large media chamber, which you can customize, so you don’t have to constantly buy replacement filters.

Marina S10 – Great for small tanks under 10 gallons. Self-priming and easy to maintain.

HOB Filter Showdown: Marineland vs Aquaclear vs Fluval. Who wins?

Canister Filter:

Marineland Magniflow  – Good brand name with great customer service.

For bigger 75 gallon or more tanks, I use the Fluval FX6 This thing is a powerhouse. Super clear water and easy to clean.

Does a fish tank filter always need to be on?

Yes. Otherwise, ammonia and nitrites that are harmful to fish will start to build up from fish waste. You should be turning over your tank 8 times per hour depending on what type and how many fish you have. Larger fish consume more and produce more waste. Smaller fish don’t create as much waste. The number of fish also weigh in as to how much waste is produced. That’s one reason why you don’t want to overcrowd the tank with too many fish.

You should be testing the water for ammonia, nitrite, and pH levels every week to see if your filter is doing the job.

Do fish tank filters use a lot of electricity?

Of all the aquarium equipment, filters are relatively low on the power usage scale. Lighting and heaters will use the most. You can lower the bill by using LED lights and keeping them off during the day. You don’t want lights on 24 hours because of the algae growth and energy consumption. Having live plants add to the cost because they need more lighting.

For an average 30 gallon tank, you would use about 150 – 200 kWh per year total.

45% of that for lighting

35% for heating the tank

12% for the filter running

8% for air pumps etc.

So let’s say you pay .12 cents per kilowatt hour. 12% of 200 kWh is 24 kWh X .12 = $2.88 per year for running a tank filter.

How long should a fish tank filter run before adding fish?

On average for a new tank that has not built up any bacteria in the filter media or substrate, you should cycle the tank about 2 weeks before you add fish. Add bacteria starter and ammonium chloride to the tank water right away to get the process going. Don’t use ammonia from the general store. You will need some test kits to measure the ammonia and nitrites in the water.

Once the nitrites and ammonia levels are at zero, you are ready to add fish.

Should a fish tank filter be fully submerged?

It depends on what type of filter you have. Hang on the back and canister filters are housed outside of the fish tank while sponge and corner filters are submerged into the tank.

Where should I put a fish tank filter?

If you are using one hang on the back filter, you should hang it just off center on the back of the tank so the water can circulate better. If you are using two hang on the back filters, then hang one on each end of the tank in the back.  For canister filters put the intake and return tube on opposite sides of the tank for better water circulation. Corner filters would be placed on one of the bottom back corners of the tank.

Fish Tank filter maintenance

Every month or so, you should replace the mechanical and chemical filter cartridges. You don’t want to replace the biological media because you will lose your beneficial bacteria. Instead, you just want to rinse whatever you use for biological filtration in old tank water. Don’t use tap water because that will kill the bacteria.

Easiest to Hardest to maintain

  1. Sponge filters
  2. Hang on the back/Power filters
  3. Canister filters
  4. Undergravel filters

How Does an Air Pump Work?

An air pump is used in conjunction with your filtration system to provide much-needed oxygen to the water in your tank. Fish need oxygen in the water to survive. The warmer the water, the less oxygen is held in the water.

Your filtration system might not be doing an adequate job of providing the oxygen to your tank, so an air pump becomes necessary. The air pump motor sits outside of the tank on a shelf or something and is plugged into an outlet. A tube is then attached from the air pump motor into the tank at the bottom. On the other end of the tube, you would attach an air stone. An air stone is just a cylindrical piece of porous substance that makes the bubbles that float up to the top. The bubbles interact with the surface, allowing oxygen into the tank water.

Ways To Modify Your Fish Tank Filter for Better Performance

Most experienced aquarists prefer to modify their filtration system to include more bacteria media or better filters for weeding out particles in the water. For biological filtration, the more surface area the better.

If you have a hang on the back filter, put a cylindrical sponge with a hole in it around the intake tube. You can get these at aquarium stores or some pet stores. Make sure the hole fits the tube. Not only does it add an extra surface area for bacteria growth, it prevents small fish and excess food from getting sucked into the filter system.

Hang on the back filters come with pretty small filters, leaving a lot of room in the chamber. If you upgrade a little and buy a bigger sponge filter to fill that area replacing the smaller filters, you would have much more surface filtration area and you wouldn’t have to keep buying new filters. You can use that sponge for a very long time as you as you rinse it once and awhile.

You could also fill the extra area with bio balls or other biological media.

Use tank water to rinse your biological media. Tap water will kill your beneficial bacteria and you will have to start all over.

For canister filtration, use non-treated egg crate sponges for your biological media. There is more surface area.

Add poly-fil from any big general store for mechanical filtration to keep the water nice and clear.


  • Get the right sized filter for your tank. Note the gallons per hour.
  • Clean out the filtration system at least once per month.
  • Don’t overcrowd your tank with too many fish.
  • Consider the type of fish and how much waste they produce. You may need a bigger filter system than required.
  • Don’t overfeed your fish.
  • Use live plants if possible. is a participant in the Amazon Affiliate Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to

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