Aquarium Filtration
Complete guide to different filtration systems for clean, healthy aquarium water
Filter Types Overview
- Internal Filters
- Sponge Filters
- External Filters
- Undergravel Filters
- Weekly cleaning for internal filters
- 3-4 month maintenance for external filters
- Choose flow rate 3-4x tank volume/hour
- Regular filter media replacement
- Monitor water flow regularly
Detailed Filter Guide
Internal Filters
These filters are great for beginners, they are relatively cheap to buy and small in size. They can work very well in smaller aquariums as long as they are maintained regularly. Each filter has a output flow rate and I would recommend that you choose a pump which will filter 3 to 4 times the volume of your water an hour.
Internal filters do not have a great volume of filter material. This will mean that the foam can clog up quite quickly, so a weekly clean is necessary. The filter is best placed in the back corner of your tank. They are normally attached to the back of your aquarium with suction pads.
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Sponge Filters
This works in a similar way to the under gravel filter. Air is forced down a plastic tube, which causes a flow of water through the sponge. This is best used as a supplement filter or a filter for a fry tank.
External Filters
These filters are for larger tanks generally 100l or over. They can also be used on smaller tanks where you want a larger flow rate or greater filter material. They are plastic containers, which you store below the aquarium. They have a pump which draws the water from the tank though a hose and flows it through the filter material then returns the water to the aquarium via another hose.
External filters have loads of room for filter materials and you can use both mechanical and chemical materials. These filters can last for about 3 or 4 months before any maintenance is required. They are more expensive than other type of filters but are well worth the money.
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Undergravel Filters
This is one of the cheapest ways to filter your tank. Under gravel filters is where water is drawn through the gravel, which sits on top of a plastic sheet placed on the bottom of your aquarium. The water is normally pumped using an air stone in a vertical tube attached to the plastic sheet. The air stone forces the water to go up the tube, which creates a current of water going from the bottom of the aquarium to the surface.
Warning: I would not recommend this method of filtration as the gravel can become easily clogged and can create a major health risk to your fish.
Filter Comparison
| Filter Type | Best For | Maintenance | Cost | Recommended |
|---|---|---|---|---|
| Internal Filters | Small tanks, beginners | Weekly | Low | âś“ Good for starters |
| Sponge Filters | Fry tanks, supplemental | Weekly | Low | âś“ Specialized use |
| External Filters | Large tanks, advanced | 3-4 months | High | âś“ Highly recommended |
| Undergravel Filters | Basic setups | Frequent | Very Low | âś— Not recommended |
The best filter depends on tank size and type of fish. Canister filters are ideal for large tanks, hang-on-back filters for medium tanks, and sponge filters for small tanks or breeding tanks.
Undergravel filters are outdated because they are difficult to clean, can trap debris, and often don’t provide sufficient biological filtration compared to modern filters.
Small, lightly stocked tanks may survive without a filter if water changes are frequent, but larger or heavily stocked tanks need a filter to maintain water quality and oxygen levels.
Undergravel filters can clog easily, are hard to clean, may reduce oxygen flow at the substrate, and generally don’t provide as effective biological or mechanical filtration as modern filters.
Yes. Filters should run continuously to maintain water quality, provide oxygenation, and support beneficial bacteria essential for fish health.
Popular and highly-rated brands include Fluval, Eheim, and AquaClear. The best choice depends on your tank size, type, and maintenance preference.
Both provide surface area for beneficial bacteria, but ceramic rings are generally better for biological filtration, while bio balls are lightweight and work well in overflow systems. The choice depends on your filter type.
Hang-on-back (HOB) filters are generally the easiest to maintain. They are simple to access, clean, and replace media, making them ideal for beginners.
There is no single “best” filter—it depends on tank size, fish type, and your maintenance style. Canister filters excel in large tanks, HOB filters are convenient for medium tanks, and sponge filters suit small or breeding setups.
Consider tank size, fish load, type of filtration needed (mechanical, biological, chemical), noise, and maintenance ease. Match the filter flow rate to your tank volume and fish species.
Bio filters can clog over time if not cleaned properly, may need occasional media replacement, and do not remove debris or chemical pollutants, so a combination with mechanical and chemical filtration is often needed.
Yes, ceramic rings are safe to place directly in an aquarium. Rinse them thoroughly before adding, especially if they are new, to remove dust or debris.