Best Aquarium Filters for a 20L Tank Setup Guide
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A 20L aquarium filter has to suit a tank of roughly 5.3 US gallons, since 20 liters converts to about that. Stand-alone filters rated specifically for 20 liters are not in the listings behind this guide, so this roundup takes a practical route: it compares small aquarium kits that already include a filter, in sizes from 1.2 to 10 gallons, and one larger canister filter as a contrast. Each entry sticks to what its own listing states, including flow figures where given.
Quick answer
- For a tank near 20 liters, the closest listed sizes are the 5-gallon Koller kit and the 6-gallon Koller AquaView 360 kit.
- Listed filter flow in these kits runs from 25 to 45 gallons per hour, so check the figure against your fish.
- Bettas and other slow swimmers do better with gentle flow; the listings themselves warn that some filters can be too strong.
- The canister filter in this list is rated for tanks up to 45 gallons, so it is far too large for 20 liters.
How to size a filter for a 20L tank
Start with the real water volume. A 20 liter tank holds about 5.3 gallons if filled to the brim, and less once you add gravel and decor. A common hobby habit is to look for a filter whose listed flow is not wildly bigger than the tank, because small fish and long-finned fish are pushed around by strong current. The listings here give flow in gallons per hour (GPH), for example 25 GPH on a 3-gallon kit and 45 GPH on a 5- and 6-gallon kit. They are the best numbers to compare.
Next, think about the media. Internal power filters in kits like these use a replaceable cartridge. The listings tell you the cartridge type and, in one case, recommend changing it every 3 to 4 weeks. That is a recurring task to plan for. For a broader look at filter choice by tank size, see best aquarium filter by tank size.
The picks at a glance
| Product | Tank volume | Listed flow | Shape and material |
|---|---|---|---|
| Koller Products 5-Gallon Aquarium Kit | 5 gallons | 45 GPH | Rectangular, plastic |
| Koller Products 6-Gallon AquaView 360 | 6 gallons | 45 GPH | Cylindrical, plastic |
| Koller Products 3-Gallon 360 | 3 gallons | 25 GPH | Cylindrical, impact-resistant plastic |
| SW Products 3-Gallon Starter Kit | 3 gallons | 25 GPH (fixed) | Round, plastic |
| hygger Horizon 8 Gallon | 8 gallons | 110 GPH, 7W | Semicircular, glass |
| minilake 10 Gallon Rimless | 10 gallons | Not stated | Rectangular, glass |
| AQUANEAT 1.2 Gallon | 1.2 gallons | Not stated | Rectangular, acrylic |
| Fluval 207 canister | Up to 45 gallons | 780 liters per hour max | Canister filter |
1. Koller Products 5-Gallon Aquarium Kit with LED and power filter
At 5 gallons, this is the nearest listed match to a 20L tank. The listing describes an internal power filter with a flow rate of 45 gallons per hour, which is stronger than the 25 GPH units in the 3-gallon kits. It uses Koller Products S replacement cartridges. The tank is one-piece, impact-resistant plastic, 16.5 inches long, 10 wide and 11.8 high, weighing 4.8 pounds. Included are the tank, a full hood, the internal filter, a filter cartridge, LED lighting, and setup instructions. The LED has 30 bulbs with white, warm, blue, and white-blue modes, and a 2, 4, or 8 hour timer with memory.
Why pick it: it matches the volume of a 20L setup and comes with the filter already fitted. The flow figure is on the high side for a tank this small, so it suits fish that handle some current more than a lone betta. The listing is aimed at tropical fish generally.
2. Koller Products 6-Gallon AquaView 360 Aquarium Kit
The 6-gallon cylindrical kit is the second closest in size. The listing gives a 45 GPH internal filter using Koller Products S cartridges, seven LED colors, and a built-in light timer with 4 hour, 8 hour, and continuous settings. The tank is impact-resistant plastic, 11 x 11 x 19.75 inches, weighing 2.5 pounds, and the listing names tropical fish, betta, cichlid, and ornamental shrimp as uses. The warranty is listed as 1 year from the manufacturer.
Why pick it: a tall cylinder gives a small footprint, which helps on a desk, and the listed uses include bettas. Check the flow against your betta’s comfort, because 45 GPH is more than the 25 GPH 3-gallon kits offer.
3. Koller Products 3-Gallon 360 Aquarium
If 20 liters is more tank than you need, this smaller kit has a 25 GPH internal filter with Koller Products XS cartridges. The listing offers seven LED colors, an impact-resistant plastic body, and dimensions of 10.25 inches in diameter by 14.75 inches high (the specs table lists 9.5 x 9.5 x 13 inches, so confirm the size before you plan a spot for it). Weight is 2.5 pounds. The listed uses include betta fish, fancy guppies, ornamental shrimp, and tropical fish.
Why pick it: the gentler listed flow suits a single betta better than the 45 GPH units. It is below 20 liters, though, since 3 gallons is about 11 liters.
4. SW Products 3-Gallon Aquarium Starter Kit
This is a round, globe-style plastic tank, 11 x 11 x 11.25 inches, 2 pounds. The listing calls the filter an ultra-quiet 25 GPH internal unit at 30 dB, fixed flow, with XS cartridges that are compatible with SW Products and Koller Products and recommended for replacement every 3 to 4 weeks. The LED has seven colors and an Always-On, 2 hour, or 4 hour timer. The listing includes care tips: rinse the tank with cold water only before first use, wipe the interior with a soft algae pad every 2 to 4 weeks, and empty the water before moving the tank.
Why pick it: a quiet, fixed-flow filter is a sensible choice for a bedroom or office betta tank. The flow cannot be adjusted, so the listing notes that LED settings do not change it.
5. hygger Horizon 8 Gallon LED Glass Aquarium Kit
This 8-gallon glass tank is larger than 20 liters, and it shows how much stronger a bigger kit filter can be. The listing gives a 7W, 110 GPH internal power filter rated for 2 to 8 gallon tanks, and it warns that the filter may be too strong for small fish shorter than 2 inches, which could be sucked in. The tank measures 19 x 11.8 x 9.6 inches, with a curved front and a 3D rockery background that takes up space; the listing says the tank holds about 6 gallons of water, and weighs about 68 pounds when full. The 18W colored LED has an external controller with time settings of 3, 6, or 12 hours and five brightness levels. The warranty is listed as one year.
Why pick it: roomier than a 20L tank, with a flow control caution that is useful to read. It is less suited to a betta unless you are willing to soften the current.
6. minilake 10 Gallon Glass Aquarium Kit
A rimless, 5mm glass tank measuring 19.7 x 10.2 x 11.8 inches and weighing 18.5 pounds. The listing says the kit includes an LED light, a filter, a lid, a magnetic glass cleaner, a manual water changer, and a fish net. It has three LED modes: white, blue, and blue and white. The listing names betta fish, goldfish, shrimp, tetras, and other small freshwater fish. It does not state the filter’s flow rate.
Why pick it: it gives a full set of maintenance tools in one box. Because flow is not stated, you will need to judge for yourself how the filter behaves, and plan to soften it if your fish are slow swimmers.
7. AQUANEAT 1.2 Gallon Tank with filter pump
The smallest tank here is 1.2 gallons, 8 x 5.25 x 7 inches, made of acrylic. The listing says the kit contains the tank, a sponge, a water filter, a 5V USB power cord, and two artificial plants, and that you need a USB power adapter rated at 5V / 2A or more, which is not included. The listing suggests it for a single betta, a couple of shrimp, snails, or a small goldfish, and notes that if the current is a bit strong you can place a pre-filter sponge on the intake. If the pump stops or flow drops, it says to remove the pump and clean the impeller and shaft assembly.
Why pick it: only if your 20L plan is really a tiny desktop setup. It is far smaller than 20 liters, so it is not a substitute for that volume. For more on this brand see AQUANEAT vs Aqueon aquariums.
8. Fluval 207 Performance Canister Filter (a much bigger option)
For contrast, the Fluval 207 is a canister filter for tanks up to 45 gallons. The listing gives a maximum flow of 780 liters per hour, 10 watts, 240 volts, a weight of 3.3 pounds, and dimensions of 11.5 x 7.6 x 11.5 inches. It describes eTEC pump technology, a vertical pre-filter cartridge, and EZ-Lift media baskets with a center handle so you can pull the media stack without emptying the canister. The listing states a manufacturer warranty.
Why mention it: if you ever plan to upgrade a 20L tank to a much larger one, this shows what canister-class filtration looks like. For a 20L tank itself it is oversized. The 240 volt rating also deserves a check against your outlet, since the listing states that figure; look at the product page for what plug and power setup it uses. See also best canister filters for aquariums.
How to pick between them
If you keep a betta
Prefer the lower listed flow. The 25 GPH 3-gallon kits are the gentlest here, and the AQUANEAT listing explicitly suggests a pre-filter sponge if the current is strong. Bigger kits can be used, but expect to tame the current.
If you want something close to 20 liters
The 5-gallon and 6-gallon Koller kits are nearest. Both list 45 GPH, so plan for a sponge or baffle if your fish dislike current.
If you want low upkeep
Check the cartridge schedule. The SW Products listing suggests a monthly cartridge change. Cartridge-based filters need new cartridges on a regular basis, which is a recurring cost of time and money.
If you want future room to grow
A 10-gallon glass kit gives more water volume, and a canister is an option for a still larger tank later.
Care habits that apply to any small tank filter
- Rinse new cartridges or sponges as the listing directs before first use.
- Clean the impeller if flow slows, as the AQUANEAT listing explains.
- Keep the intake clear of plants and decor.
- Soften strong currents with a sponge or by redirecting the outlet.
- Use a power adapter that matches the listing, if the kit needs a separate one.
For more ideas on fine filter pads, read fine filter pads for aquarium: how to choose and cut to fit.
FAQ
How many gallons is a 20L aquarium?
About 5.3 US gallons. In practice the usable volume is lower once gravel and decor go in.
Which listed kit is closest to 20 liters?
The Koller 5-gallon kit at 5 gallons, and the Koller 6-gallon AquaView 360 at 6 gallons.
Is 45 GPH too strong for a betta?
The listings do not say. The hygger listing warns that its 110 GPH filter may suck in small fish, so stronger units call for care. A sponge on the intake is a common fix.
Do I need a canister filter for 20 liters?
No. The Fluval 207 listing says it is for tanks up to 45 gallons.
How often should I change cartridges?
The SW Products listing recommends every 3 to 4 weeks for its XS cartridge and says to replace monthly for best water quality. Follow the instructions of your own filter.
Are these kits suitable for any fish?
The listings name tropical fish, bettas, shrimp, tetras, and small goldfish in various cases. Check each listing’s own uses and the adult size of your fish.
Bottom line
For a 20L tank, choose a kit around 5 to 6 gallons with a filter whose listed flow your fish can handle, and use the 25 GPH units for gentle-water fish. Skip the canister unless your tank is far bigger.
