Internal Filter Aquarium: The Complete Guide for Fishkeepers

Aquarium keeping is both a rewarding and relaxing hobby, but maintaining water quality is one of the biggest responsibilities for any aquarist. Clean, well-filtered water ensures that your fish, plants, and other aquatic inhabitants remain healthy. One of the most commonly used filtration systems for small to medium-sized aquariums is the internal filter aquarium setup.

This guide will cover everything you need to know about internal aquarium filters, including how they work, their pros and cons, setup instructions, maintenance tips, and comparisons with other types of filtration systems.

What Is an Internal Filter Aquarium?

An internal aquarium filter is a type of filtration unit that sits inside the tank rather than outside. Unlike hang-on-back (HOB) filters or canister filters, which are external, an internal filter is fully submerged in the water. It usually attaches to the glass using suction cups or brackets and draws water through different filtration media before releasing clean water back into the tank.

These filters are popular among beginners and hobbyists with nano tanks, small aquariums, breeding tanks, and quarantine tanks, where space and ease of maintenance are priorities.

How Does an Internal Aquarium Filter Work?

Internal filters work using a simple yet effective mechanism:

1. Water Intake – The filter sucks in dirty aquarium water through slots or holes at the bottom or sides.
2. Filtration Media – The water passes through filter media that provide mechanical, chemical, and biological filtration:
   • Mechanical filtration: Sponge or foam traps debris, uneaten food, and fish waste.
   • Chemical filtration: Activated carbon or special resins remove toxins, odors, and discoloration.
   • Biological filtration: Beneficial bacteria colonies break down harmful ammonia and nitrites into less toxic nitrates.
3. Water Outlet – Clean water is pushed back into the aquarium, often with an adjustable flow rate for better circulation.

Benefits of Internal Filters in Aquariums

1. Compact and Space-Saving
   Internal filters are small and discreet, making them perfect for small aquariums or aquascapes where aesthetics matter.
2. Easy Installation
   Unlike canister filters that require hoses and plumbing, internal filters are simple to set up—just stick them inside the tank and plug them in.
3. Cost-Effective
   They are generally cheaper than external filters, making them ideal for beginners.
4. Quiet Operation
   Since they are submerged, internal filters tend to produce less noise compared to hang-on-back filters.
5. Safe for Fry and Shrimp
   Internal sponge filters, in particular, provide gentle filtration that doesn’t suck up small fish, fry, or shrimp.
6. Added Water Circulation and Aeration
   Many internal filters come with spray bars or adjustable outlets that improve oxygen levels in the tank.

Drawbacks of Internal Aquarium Filters

1. Takes Up Tank Space
   Being inside the tank, internal filters occupy swimming space, which can be an issue in small aquariums.
2. Limited Filtration Capacity
   Internal filters are not as powerful as canister or sump systems, making them less effective for large tanks.
3. Frequent Maintenance
   Since they trap debris quickly, the filter media must be cleaned more often.
4. Visible in the Tank
   Some aquarists dislike the look of equipment inside their aquascape.

Types of Internal Aquarium Filters

There are several designs of internal filters, each catering to different aquarium needs:

1. Sponge Filters
   • Powered by an air pump, sponge filters provide gentle filtration and are commonly used in breeding tanks and shrimp tanks.
   • They are excellent for biological filtration.
2. Corner Filters
   • Small filters placed in the corner of the tank.
   • Work similarly to sponge filters but may include chemical media as well.
3. Box Filters
   • Small plastic boxes with customizable filter media.
   • Popular in older aquarium setups and fry tanks.
4. Power Internal Filters
   • Submersible filters with built-in pumps that provide stronger mechanical and chemical filtration.
   • Good for small to medium community tanks.
5. Internal UV Filters
   • Some advanced internal filters have UV sterilizers to kill harmful bacteria and algae spores.

How to Set Up an Internal Filter in an Aquarium

1. Choose the Right Size
   • Pick a filter suitable for your tank’s water volume. Most internal filters list recommended tank sizes on the packaging.
2. Placement in the Tank
   • Install the filter near a corner or along the back wall.
   • Ensure the water outlet is directed to maximize circulation.
3. Add Filter Media
   • Use sponge, ceramic rings, or activated carbon depending on your filtration needs.
4. Attach with Suction Cups/Brackets
   • Secure the filter firmly to prevent it from floating or moving.
5. Prime and Start
   • Submerge the filter, plug it in, and adjust the flow rate.

Maintenance of Internal Filters

To keep your internal filter running efficiently, follow these maintenance practices:

• Weekly Rinse: Rinse sponges or filter pads in tank water (not tap water) to preserve beneficial bacteria.
• Replace Media: Activated carbon should be replaced every 3–4 weeks. Sponges last longer but may eventually need replacement.
• Check Flow Rate: A decrease in water flow indicates clogging and requires cleaning.
• Avoid Overcleaning: Do not wash all media at once, as this can destroy beneficial bacteria colonies.

Internal Filter vs. Other Aquarium Filtration Systems

Best Aquarium Practices with Internal Filters

1. Combine internal filters with live plants for a balanced ecosystem.
2. Ensure proper stocking—overcrowding leads to more waste than an internal filter can handle.
3. Supplement with water changes (20–30% weekly) to maintain water quality.
4. Monitor ammonia, nitrite, and nitrate levels regularly.

Conclusion

An internal filter aquarium setup is one of the most beginner-friendly and cost-effective filtration methods available. While it may not be powerful enough for very large tanks, it provides reliable water quality for small to medium aquariums, breeding tanks, and shrimp setups. With proper setup and maintenance, an internal filter will keep your aquatic pets healthy and your aquarium water crystal clear.

FAQs about Internal Filter Aquarium

Q1: Is an internal filter enough for my aquarium?
Yes, for small to medium-sized tanks (up to 50 gallons), an internal filter is sufficient. For larger aquariums, consider a canister or sump system.

Q2: How often should I clean my internal filter?
Rinse the sponge or filter media every 1–2 weeks in aquarium water. Replace chemical media like carbon monthly.

Q3: Can I run two internal filters in one aquarium?
Yes, especially in larger tanks. Running two filters improves water circulation and biological capacity.

Q4: Do internal filters provide oxygen to the tank?
Yes, many internal filters agitate the water surface or include air attachments, which help increase oxygen levels.

Q5: Are sponge filters better than internal power filters?
Sponge filters are best for fry, shrimp, and gentle filtration, while internal power filters are better for community aquariums that need stronger filtration.

Q6: Can I hide my internal filter in aquascaping?
Yes, you can disguise it with rocks, driftwood, or plants, as long as water flow is not blocked.