3 Types of Aquarium Filtration Every Fishkeeper Needs

Filtration is one of the most important parts of keeping fish. But it can also be confusing. Many people think filters are only for cleaning water. That’s not true! There are three main types of filtration you should know:

• Mechanical Filtration
• Biological Filtration
• Chemical Filtration

Let’s look at what each one does and why it matters.

1. Biological Filtration 

This is the most important type of filtration. If you get this part right, the rest is easier.

Biological filtration is all about helpful bacteria. These bacteria grow on surfaces in your tank. They break down fish waste through a process called the nitrogen cycle.

Here’s how it works:

• Fish produce ammonia (a toxic waste).
• One type of bacteria turns ammonia into nitrite (also harmful).
• Another type turns nitrite into nitrate (less harmful).
• Plants or water changes remove the nitrate.

You don’t always need a filter for this. The bacteria can grow on rocks, plants, and even the gravel. But if your tank has a lot of fish, a filter helps a lot. It gives bacteria more space and helps move oxygen through the water.

Example:
In our 75-gallon Mbuna tank, we use a canister filter. The fish make a lot of waste. Without the filter, they would not get enough oxygen, and waste would build up.
But in our 50-gallon planted tank with only a few fish, we don’t need much filtration. A filter would help, but it’s not required.

Tip: Most filters today have more than enough room for bacteria. In our fish room, even tanks with 100 small fish use only one sponge filter—and we never have problems with ammonia.

2. Mechanical Filtration 

Mechanical filtration removes debris. It pulls out bits of food, plant leaves, and fish waste floating in the water.

If your tank is healthy but looks cloudy, this type of filtration can help.

Best Tools for This Job:

• Canister Filters – Great
• Sumps – Very Good
• Hang-on-Back Filters – Also Good

Not Great for This Job:

• Sponge Filters
• Matten Filters
• Box Filters

Sponge filters do a little mechanical filtering. But they must be cleaned often or they won’t work well. In our canister filters, we use sponge pads and filter floss. This traps fine particles and makes the water look clear.

Ask Yourself:
Do I want my water to look clean and clear?
If yes, mechanical filtration is a good idea.

3. Chemical Filtration 

Chemical filtration uses special materials to clean the water. This includes things like:

• Activated Carbon
• Purigen

These products remove chemicals like chlorine, medicine, or metals.

When Should You Use It?

• If you have well water with metals
• If you’ve used medicine and want to remove it
• If your water smells or looks odd

In our tanks, we use tap water and a dechlorinator. We haven’t used chemical filters in over 10 years. They’re also more costly than sponge or floss media.

Some filters can’t use chemical media. For example:

• Sponge and Matten filters can’t hold them easily.
• Box filters can hold a little.
• Hang-on-Back, Canister, and Sump filters work best.

Here’s a quick guide to help you:

    Focus on biological filtration—it keeps your fish safe.
    Use mechanical filtration—if you want clear water.
    Skip chemical filtration—unless you have a special need.

Even our 125-gallon Geophagus tank could run with only a sponge filter. That would take care of the biological part. But we use canisters too—because we like crystal-clear water.

One Last Tip:
Clean your filter media often. A dirty filter won’t work well. The tank will look cloudy, and waste will build up.

FAQ

1. Do I really need a filter in my aquarium?
Not always. If your tank has few fish and lots of plants, bacteria can grow on surfaces and keep the water safe. But a filter helps a lot in busy tanks.

2. What’s the most important type of filtration?
Biological filtration is the most important. It removes toxic waste from the water using helpful bacteria that grow on surfaces.

3. Why does my water look cloudy even with a filter?
Your filter may need cleaning or better mechanical media like sponge or floss. Mechanical filtration helps trap dirt and floating particles.

4. When should I use chemical filtration?
Use it after treating fish with medicine or if your tap water has heavy metals. Most tanks don’t need it all the time.