Internal filters, also known as internal power filters, work similarly to external power filters but they are meant to be submerged inside aquariums. When an internal filter works, water is drawn through the filter chamber by a water pump and then it is purified by various types of filter media. The most common forms of internal filters use foams as the major mechanical material and often a cartridge with activated carbon to remove organic wastes dissolved in the water.
Internal power filters provide a good replacement for internal air driven box filters and sponge filters because they can accommodate a larger amount of filter media for better filtration and less maintenance. They are also easy to hide from view using decorations and plants, so they do not ruin the appeal of your aquarium. Starter hobbyists like to use these filters because they are very simple and easy to install and clean.
Here are some of the recommended internal filters for small to large aquariums.
- Marina I25 internal filter for small tanks up to 6.6 gallons
- Tetra Whisper 10i in-tank filter for tanks up to 10 gallons
- Fluval U4 underwater filter for 34-65 gallon fish tanks
- Aqueon Quietflow internal power filter AT30
- Penn Plax Cascade 600 submersible aquarium filter
- Ca 900 internal aquarium filter for tanks up to 50 gallons
- SunSun 528-GPH internal filter for turtle tanks
Marina I25 internal filter for small tanks up to 6.6 gallons(4.5/5 by editor)Check on Amazon.com
- Max flow rate: 26.4 US gallons per hour (100 L/H)
- Ideal for: aquariums up to 6.6 gallons (25 l)
- Media: Marina I25 replacement power cartridge.
This clip-on filter is suitable for small tanks with up to 6.6 gallons of water. The filter works on a unique mechanism that allows water to enter the center of the cartridge. This allows the internal filter to work effectively at eliminating odor and toxic ammonia in the water. The filter operates so quietly, you can even have your tank beside your bed and not worry about the noise.
The Marina I25 power cartridge is so powerful and worth for the money. It includes zeolite chamber, activated carbon chamber, and floss layer that respectively perform biological, chemical, and finally mechanical to completely purify the water and keep your fish healthy. Changing the cartridge is easy and fast that needs to be performed every four weeks.
Tetra Whisper 10i in-tank filter for tanks up to 10 gallons(4/5 by editor)Check on Amazon.com
- Flow rate: 80 GPH
- Used for: tanks up to 10 gallons
- Media: medium Whisper bio-bag cartridge
- Available sizes:
- Tetra Whisper 20i – 125 GPH – for tanks up to 20 gallons
- Tetra Whisper 40i – 170 GPH – for tanks up to 40 gallons.
This in-tank filter is quiet and well-suited for small aquariums holding up to 10 gallons. It uses a medium Whisper bio-bag cartridge and a patented Bio-scrubber pad to provide a three-stage filtration. The Whisper bio-bag cartridge is a floss pad filled with activated carbon to eliminate waste particles, odors, and discoloration in aquarium water. The Bio-scrubber pad provides the house for helpful bacteria to colonize and performs biological filtration processing nitrogenous toxins from fish waste and uneaten food.
The installation of this filter is very easy using suction cups included. You can place the filter at high or low water levels as you want. It can also be used as a waterfall for low-water tanks or turtle tanks. Cleaning up and maintenance is a breeze, too. The bio-bag cartridge needs to be changed every month.
Fluval U4 underwater filter for 34-65 gallon fish tanks(4.5/5 by editor)Check on Amazon.com
- Out put: 260 US gallons per hour, adjustable
- Ideal for: fresh/marine water environments, reptile turtle tanks
- Media: 2 foam pads, 2 poly/carbon cartridges, BioMax biological rings
- In this Fluval U series: Fluval U1 (tanks up to 15 gallons), U2 (for 12-30 gal), U3 (for 24-40 gal).
Tank owners will like this in-tank filter for its large filtration chamber and better performance like external filters. This is suitable for tanks mounted against the wall, or any other configuration that would not work with external filters. It is a silent and efficient solution to keep your fish happy and healthy because it provides optimal biological filtration. You can use this as a stand-alone filter or as a supplemental filter for a bigger tank.
The filter comes with 2 foam pads that take care of large particles, 2 poly/carbon cartridges, and 90 grams BioMax. These filter materials are the most advanced ones in the market from Hagen Fluval. Inside the filter, they are organized to create a multi-stage filtration system from foam pad to carbon cartridge and finally to Biomax. In the first stage, the foam pad mechanically traps large particles. In the second stage, the carbon cartridge traps fine debris and eliminates impurities to improve water clarity and smell. Finally, Biomax provides the best environment for helpful bacteria to process nitrogenous toxins to protect your aquarium inhabitants.
A unique feature of the Fluval U4 is that it returns water to the aquarium through three ways including top output, bottom output, and an integrated spray bar for better water filtration and circulation. There is an adjustment knob on the top output for you to adjust the water output to achieve gentle flow and quiet operation.
Aqueon Quietflow internal power filter AT30(5/5 by editor)Check on Amazon.com
- Flow rate: 142 GPH
- Ideal for: aquariums or terrariums up to 30 gallons
- Media: large Aqueon replacement internal filter cartridge
- Other models: AT10 (57 GPH – up to 10 gal), AT15 (66 GPH – up to 15 gal), AT40 (155 GPH – up to 40 gal)
If you’re looking for an in-tank filter that’s versatile, look no further. Aqueon gives you this fully submerged filter that can be positioned horizontally or vertically. You can adjust the return flow rate, as well as the height and direction of water return. What makes it loved by many hobbyists is the very large filter chamber for the free of using filter media. You can use your favorite filter materials or ones coming with the product package.
The filter uses a large internal filter cartridge from Aqueon to give you a three-stage filtration including mechanical, chemical and biological. Dense foam for trapping larger particles, activated carbon to eliminate chemical toxins, odors and discolorations, and patented BioGrid to take care of ammonia and nitrites. This is an ideal choice for aquariums or reptile tanks up to 30 gallons.
Penn Plax Cascade 600 submersible aquarium filter(5/5 by editor)Check on Amazon.com
- Flow rate: 175 GPH
- Used for: 20-50 gallon fish tanks (fresh/salt water), reptile turtle terrariums
- Media: bio-foam, activated carbon cartridge
- Other sizes:
- Penn Plax Cascade 170 (45 GPH) for tanks up to 5 gallons
- Penn Plax Cascade 300 (70 GPH) for tanks up to 10 gallons
- Penn Plax Cascade 400 (110 GPH) for 10-20 gallon tanks.
If you want an in-tank filter that offers advanced physical, chemical, and biological filtration while increasing the aeration of your fish tank, Penn Plax Cascade 600 is a submersible filter for you. Able to deliver up to 175 gallons per hour of flow rate, the filter is an ideal choice for 20-50 gallon fish tanks or terrariums.
The Penn Plax Cascade 600 internal filter is able to clean your aquarium at different levels. It is equipped with an activated carbon cartridge to get rid of harmful chemicals and toxins, odors, discoloration, and other contaminants in the water. It also comes with an internal sponge that improves the colonization of beneficial aerobic bacteria, which provides a healthy balance in the aquarium environment. Thanks to its large capacity, you can choose your favorite filter media to use.
The filter features a pump head that lets you adjust the water flow and direction. There comes a spray bar in the package that helps to divide the output water into many small streams, which enhances your aquarium aeration and biological filtration. You can place the filter vertically or horizontally and make it hidden from view.
Ca 900 internal aquarium filter for tanks up to 50 gallons(5/5 by editor)Check on Amazon.com
- Flow rate: 235 GPH
- Ideal for: aquariums or turtle tanks up to 50 gallons
- Media: washable sponge
- Other sizes: Ca 750 internal aquarium filter (200 GPH) for 30-50 gallon tanks
This in-tank filter is a good choice for the filtration system of fish or turtle tanks up to 50 gallons. It has a 235 GPH output and is ideal for both freshwater and saltwater environments. With dimensions of 3 1/2″ x 2 1/2″ x 12 1/2″, it can fit most tanks with ease. It also has an air line hose for oxygen input, which increases the aeration of your tank and makes your fish and turtles active and healthy.
SunSun 528-GPH internal filter for turtle tanks(4.5/5 by editor)Check on Amazon.com
- Flow rate: 528 GPH
- Ideal for: turtle tanks, freshwater or saltwater
- Media: sponge pre-filter media, carbon basket
- Other sizes: SunSun 210-GPH, SunSun 396-GPH, SunSun 845-GPH.
This filter features a dual intake system, one comes from the bottom of the filter, and the other one from the top plays the role as a surface skimmer, which keeps the water surface free of dirty particles. The system is composed of a 1-pump, 2-impeller return system that provides optimal water flow. You can also configure the filter to include a spray bar.
It comes with a sponge pre-filter media and a carbon basket filled with premium carbon, which keep your aquarium water clean and clear. With a powerful filtration of up to 528 gallons per hour, this is an ideal internal filter you should use for your turtle tank.