Although a 5-gallon aquarium is only a small one, you still need to use a proper filtration system. Many beginners to the hobby assume that you don’t need fish tank filters in small aquariums and nano tanks, but that’s not the case. All you need to do is put some fresh tap water into your nano tank every week or two. Right?
No! Fish waste, leftover food, and other impurities can quickly accumulate in a small tank, polluting the water and quickly poisoning your fish. And, did you know that tap water contains ammonia, which will burn your fishes’ gills?!
So, we wrote this comprehensive guide on how to choose the best filter for a 5-gallon tank and much more too!
Quick Comparisons Of The 7 Best 5-Gallon Aquarium Filters
|Tetra Whisper Internal Aquarium||View Product|
|AquaClear Aquarium Power Filters||View Product|
|Marina I25 Internal Filter||View Product|
|Penn Plax Small World Pump||View Product|
|Aqueon Power Filter||View Product|
|Lee's Undergravel Filter||View Product|
|Zoo Med Canister Filter||View Product|
Why Do You Need A Filter System In A 5-Gallon Aquarium?
You often see betta fish living in vases or bowls with no filtration system whatsoever. So, it is technically possible for a fish to survive in a small tank without a filter. However, it’s very difficult and labor-intensive to keep a very small aquarium clean without a filter system. Also, small tanks tend to become stagnant and dirty much quicker than larger ones.
How so? Well, think of it this way. If you put a teaspoon of bleach into a 30-gallon container full of water, the solution you create will be much weaker than if you put the same amount of bleach into a 5-gallon tank. The same principle applies to the harmful chemicals that are produced when fish waste, leftover food, and dead plant matter decompose. So, you can see that a small tank will quickly become a toxic soup for your poor fish to swim in.
In nature, that waste would be eaten by beneficial bacteria, swept away by the current, and heavily diluted by rainwater. However, your tank is a closed environment, where a filtration system essentially does that job. Without filtration, ammonia, nitrites, and nitrates quickly build up in the water, poisoning your fish.
How Do Aquarium Filtration Systems Work?
All filtration systems work in essentially the same way, using mechanical, biological, and chemical elements or a combination thereof.
Mechanical filtration works by drawing the aquarium water across a filter pad, floss, or sponge that traps floating debris. The filter media is kept inside a filter casing and provides a platform for colonies of bacteria that consume those waste products.
A good flow rate is essential and is, to some extent, dependent on the density of the filter media that you choose. Generally, filter media with a very fine pore size will quickly clog, whereas media with a large pore size won’t trap debris efficiently. If the media is too dense for the capacity of the filter pump, the flow rate won’t be powerful enough.
Mechanical filters must be cleaned and replaced regularly to keep the bacterial colonies healthy and prevent the accumulation of debris in the media.
The biological element of a filtration system uses living bacteria that break down the waste products that are drawn through the filter media by the mechanical element of the filter system. Colonies of bacteria live on the filter media inside the filter system. Those bacteria also grow on the substrate, on plants, and on the tank glass within the tank itself.
Chemical filtration uses activated carbon or resin to remove dissolved particulate from the water. Activated carbon filters contain millions of pores that collect dissolved substances such as heavy metals, removing them from the water. Over time, the pores fill up, and you need to replace the filter sheet.
One major drawback of using chemical filtration is that it removes many fish medications, too, such as antibiotics. So, if you do need to treat the water, you must remove the carbon element from your filtration system first.
Types Of Filter For A 5-Gallon Tank
There are several styles of filters that you can use with a small tank.
HOB (Hang-On-Back) Filters
HOB filters are an extremely popular design of the filter system, largely because they are external to the tank, rather than taking up valuable space inside the aquarium, which is a major consideration with a small setup.
Other advantages of HOBs include:
- An air pump integrated into the design, so you don’t need a separate power source.
- HOBs are super-easy to install. Just plug the unit in, switch it on, and you’re good to go!
- Maintenance is relatively hassle-free because all the filter media and the impeller are easily accessible.
- HOBs generally offer three-stage filtration and many are customizable.
- The intake and flow rates are often adjustable.
You can read an in-depth review of HOB filters in our comprehensive article at this link.
Canister filters are another form of external filtration unit that you place out of sight in your aquarium cabinet. The other main features of a canister filter include:
- Canister filtration systems offer three-stage filtration.
- These are large units that are very efficient at keeping the tank water clean and safe for your fish.
- The flow rate is usually adjustable.
- Canister filters can be fiddly to set up and time-consuming to maintain.
For a detailed overview of canister filters and how they work, check out this article.
An undergravel filter sits on the bottom of the aquarium underneath the substrate. Water is drawn down through the gravel, taking waste material with it to feed the beneficial bacteria that live on the filter plate. The water is then pulled up through two uptake tubes that are fixed to the back corners of the filter plate before flowing back into the tank.
Although undergravel filters do create thriving bacterial colonies and a very efficient biological filtration system, they do not contain filter media, and waste products end up trapped in the gravel and underneath the filter plate.
You can read more about undergravel filters and check out some product reviews at this link.
Internal filters reside within the tank, usually fixed to the aquarium wall by means of suction cups or hooks. The filter unit is usually a box that contains various three-stage filter media, the pump motor, and the impeller.
The main downside to using an internal filter in a 5-gallon tank is that the unit takes up space. Also, you need to replace the filter media regularly, which can be expensive.
How Often Should You Clean A Small Filter?
The frequency with which you clean your filter largely depends on the filter system that you have chosen. Generally, HOBs and canister filters only require cleaning once every three weeks to a month to keep them free from gunk so that the flow rate remains good and the bacteria in the biological element of the filter system remain healthy.
The same applies to internal filter systems unless you have a sponge filter, which will need cleaning every two weeks or so. Undergravel filters should be removed from the tank and cleaned annually, which is a big job when you consider that you’ll need to empty the tank completely to get at the filter plate.
How Do You Reduce The Flow On A Filter?
All aquarium filters have a flow rate that is measured at GPH or Gallons Per Hour. That means that the filter pump circulates the water in the tank a certain number of times every hour. We recommend that you choose a filter that turns over your aquarium volume at least four times per hour. So, if you have a 5-gallon tank, you want a unit with a flow rate of around 20 GPH.
The flow rate must be powerful enough to disturb particles of solid debris and draw them into the filter media instead of allowing the waste to fall down into the substrate. However, if the flow rate is too powerful, it can be very disruptive in the aquarium.
How Much Is Too Much?
The amount of flow that you want depends on your particular setup and the fish species that you keep. For example, if you keep a nano tank with a betta fish, you don’t want to generate too much water movement, or your pet will struggle to swim. Fancy goldfish are also very poor swimmers who don’t appreciate a turbulent current.
Also, if you have a planted tank, too much flow can buffet your plants so much that they become damaged or even uprooted, leaving you continually replanting or replacing them.
Adjusting The Flow Pattern
Many times, it’s not the actual flow rate that is the problem, but the flow pattern. So, you don’t want to compromise the filter’s ability to keep your tank clean, but you don’t want to stress your fish either. Therefore, you need to adjust the pattern of the flow.
Rearrange rocks and pieces of driftwood to create buffers that can redirect a strong flow. Many fish like to rest in areas of calm water, and buffering the flow in this way can help to provide those all-important safety zones.
Dense banks of living and silk plants can also help to disrupt flow patterns, creating calm zones where fish can rest. Broadleaf species work especially well for that task and are less likely to be damaged or uprooted in the current than flimsier specimens.
Adjust The Flow Control On HOBs
HOB filters are fitted with a flow-restricting valve on the intake tube. By adjusting that control, you can reduce the flow of water into the filter and calm the water. However, filter adjustment also reduces the GPH of the unit, so the water circulation around the tank will be reduced.
Adjust The Flow Control On HOBs
If you have a canister filter, it may have a flow control valve that you can adjust to reduce the flow without affecting the unit’s efficacy.
Use Flow Diverters
Some canister filters have an outlet nozzle that enables you to divert the water flow in two different directions. You can also buy flow diverters to add to some designs of internal filters, although some brands have them included in the design. Splitting the flow reduces the power of the current instantly without compromising the degree of circulation.
If you have a canister filtration system, you could use recirculation to divert some of the flow back to the sump. To do that, you need to add a “T” and valves to your unit to send some of the water back to the aquarium while diverting the remainder to the sump. However, that will reduce the GPH flow through the tank, as well as calming the current. So, there is a compromise to that approach.
How To Choose A Filter For A 5-Gallon Tank
When I buy a new filtration system for a 5-gallon nano tank, I always consider the following points:
The flow rate that you want largely depends on the species of fish that you intend to keep. Ideally, you need to choose a filter that has an adjustable flow rate or redirection feature. That’s especially important in a small tank where too much current and water turbulence could create a washing machine effect for your poor fish!
Ease Of Maintenance
I prefer to choose a filter that has an easily accessible impeller and media. I recently changed both my filters from units that took media cartridges to a simple sponge filter design. Not only are the new filters much quicker and easier to clean, but I also don’t have the expense of buying replacement cartridges every month.
The filtration media that you choose is really a matter of personal choice. However, having all three methods of filtration assures you of the best water quality for your aquarium. Just bear in mind that some brands of filter cartridges can work out costly in the long run, depending on the frequency of replacement and their price.
Just like an aquarium heater, the reliability of the filtration system is of paramount importance. You need to know that the motor and pump are reliable and will restart immediately following a power outage. Also, you don’t want a filter media that clogs up or disintegrates.
Check out buyer reviews to find out about other users’ experiences before buying a filter unit.
Best 5-Gallon Aquarium Filters – Quick Product Reviews
Now that you know more about how to choose a filter for a 5-gallon tank check out these reviews of seven of our favorite filter systems for small setups.
1. Tetra Whisper Internal Aquarium Power Filter With BioScrubber
- Internal box filter
- 4.25 x 4 x 8 inches
- Up to 10 gallons
Tetra’s Whisper Internal Power Filter with BioScrubber is an innovative submersible filter that has a three-stage filtration system, including a double-sided Bio-Bag mesh that traps waste and debris and activated carbon that prevents water discoloration and absorbs odors. This filter is designed with easy maintenance and convenience in mind, featuring an anti-clog design and super-efficient easy access biological media.
The filter’s motor sits underneath the water, helping to keep the unit super-quiet while offering the same superior performance of an external filter. Flow direction and rate are easy to customize for your tank thanks to the waterfall feature.
The unit is supplied with a pre-assembled Bio-Bag filter cartridge to get you started.
2. AquaClear Aquarium Power Filters, Model 20
- HOB filter
- 4.48 x 7 x 6.5 inches
- Up to 20 gallons
The Aquaclear Power is a HOB external filter that is recommended for aquariums up to 20 gallons and kicks out an impressive 100 GPH, offering quiet, reliable, and efficient biological and mechanical filtration. Some filter media is included with the unit.
This filter is designed as a refiltration system that provides superior water contact time with the filter media, helping to keep the water crystal clear and providing bacterial colonies with plenty of oxygen so that they thrive. The efficiency of the system means that running costs are kept down. Despite that, you still get up to seven times more filtration volume, and the flow rate is adjustable, too, making this filter a great choice for a small aquarium.
3. Marina I25 Internal Filter
- Internal box filter
- 3 x 3.2 x 8 inches
- Up to 6.6 gallons
The Marina I25 Internal Filter is designed for use with small tanks up to 6.6-gallons, making this a great choice if you have a betta or nano tank. I love the clever clip-on design of this filtration system, although you do get suction cups, too, giving you the choice of what fixing method to use.
The filter’s motor is submerged under the water, so operation is extremely quiet. The unit takes filter cartridges that enable three-stage filtration, keeping the water free from ammonia, odors, heavy metals, and floating debris. That means that your aquarium stays crystal clear and safe for your fish. The filter cartridges are very easy to remove and replace, and you get one free replacement cartridge with the unit.
4. Penn Plax Small World Pump And Filter Kit
- Internal filter
- 7 x 2 x 10 inches
- Up to 5 gallons
The Small World filter has to be the smallest filtration unit I’ve ever seen! This system is specifically designed for small tanks and fishbowls up to 5-gallons. In the box, you get an air pump, filter unit, tubing, and a mounting bracket. Filtration consists of a carbon-zeolite cartridge to remove chemicals and heavy metals from the water and a foam block for biological and mechanical filtration.
On the downside, some users have mentioned that the unit isn’t powerful enough for a 5-gallon betta tank. Also, you need to prime the unit, and to set it up is somewhat fiddly, thanks to the filter system’s tiny size. The same applies to maintenance, as removing the filter sponge is tricky and can be time-consuming.
5. Aqueon X-Small QuietFlow E Internal Power Filter, 3 Gallon
- Internal filter
- 2.75 x 2.75 x 6.81 inches
- Up to 3 gallons
Designed for use with smaller tanks up to 3-gallons yet still boasting an impressive 25 GPH flow rate, the Aqueon QuietFlow E Internal Power Filter small water filter is quick and easy to install and self-priming. Hanging clips are provided for framed tanks, as well as suction cups to accommodate frameless aquariums.
The unit is supplied with dual-sided filter cartridges that provide mechanical and chemical filtration, keeping your aquarium water clean and safe for your fish. There’s no need to worry if your area suffers a power outage while you’re not home, as this filtration unit has an automatic restart function that gets the pump going again once the power has been restored.
For peace of mind, you get a lifetime warranty with the product.
6. Lee’s 5-1/2 Economy Undergravel Filter
- Internal undergravel filter
- 8 x 16 inches
- Up to 5 gallon
Lee’s Economy Undergravel Filter gives you a hassle-free biological filter with a raised flat plate design that allows for much better water circulation than some other designs. Better water flow ensures that the bacteria in your biological filter get plenty of oxygen, and the risk of clogging is much reduced.
This is a single-piece unit, so it’s imperative that you get the correct size for your tank. The materials used are pretty strong and robust, so the filter is safe for use in saltwater and brackish tanks. Another big plus point for this kind of filter is that it can cycle much more quickly than other styles of filtration system, so you won’t have to wait as long before adding the first fish to your tank. You can use this system with acrylic, glass, and even a plastic fish tank.
Although you can add an activated carbon filter bag to the system, there’s no pump supplied, so you will need to supply your own.
7. Zoo Med Nano 10 External Canister Filter
- External canister filter
- 8 x 16 inches
- 2 to 10 gallons
I’m going to say right off the bat that this unit isn’t as powerful as the manufacturer claims, according to the majority of customer reviews that I’ve read. That said, if you have a 5-gallon tank, the 30 GPH capacity of the unit is more than adequate. Also, the unit comes with a spray bar, making it ideal for nano tanks with bettas and other species that don’t appreciate too much water movement.
The three-stage filtration provided by the unit ensures that your tank will stay clean and safe for your fish. The unit is easy and quick to set up and prime, and the external design means that you won’t be taking up valuable space inside your tank. Specially calibrated anti-vibration bushes help to keep noise to a minimum. Included with the unit are both a carbon bag and some ceramic biological filter media.
Of the filtration systems that we reviewed in this guide, the Aqueon X-Small QuietFlow E Internal Power Filter comes out on top.
This neat filter is ideal for small tanks yet still produces a good flow rate to keep the environment clean and fresh for your fish. The unit is self-priming, provides three-stage filtration, and comes with dual-sided filter cartridges included.
We particularly like the automatic restart function that ensures that the pump will restart after a power outage, giving you peace of mind if you’re out at work or away on vacation. Also, you get a lifetime warranty, which is always nice to have.