Regardless of its size, every freshwater and saltwater fish tank needs an efficient filtration system that provides enough biological and mechanical functionality to keep the water clean and well-oxygenated.
Without a doubt, choosing the right filter for a large aquarium is a challenge. In this article, we explain how to choose the best aquarium filter for large tanks, as well as give you product reviews of our top five filtration systems that are ideal for a large setup.
What Is Considered A Large Tank?
A large fish tank is generally defined as one with a capacity of 75 gallons or more. Most large home aquariums are between 75 and 100 gallons, although you can get sizes in between, and if you have the space, you can buy a huge tank that holds 400 gallons or even more.
However, it is worth considering that the larger the tank, the more powerful the filtration system you need, and maintaining a very large aquarium requires more time and work than for a smaller setup. You can check out our reviews on the best 5 gallon aquarium filter for smaller aquariums.
How much filtration is needed for large tanks?
So how much filtration is needed for large tanks?
The general rule of thumb for filtration rates is that all the water contained in your aquarium passes through your filtration system at least four times per hour. So a 100 gallon tank requires a flow rate of at least 400 gallons per hour (GPH).
When I buy a filter for my fish tank, I always choose a unit that provides a slightly higher GPH rate than I need. That extra flow ensures that the water has all the oxygen my fish need, and the filtration unit can cope with the amount of waste that dirty goldfish produce.
The GPH rate varies greatly, depending on the strength and type of filter, the efficiency of the unit, and its condition. If you decide to go for a higher GPH, that’s great as it means the conditions in your aquarium will be better for your fish. However, you need to consider how the power of the flow through the tank will affect your fish and plants.
For example, betta fish don’t like a lot of movement in the water and quickly become stressed if they can’t swim comfortably. One solution to that problem is to dampen the flow with plants or decorations, or choose a filtration unit that has directional valves that you can adjust to suit your needs.
GPH and rotation rate
The turnover rate is not the same as the GPH. The turnover rate describes the efficiency of the filtration unit and its pump, rather than the amount of water the system can circulate around the tank.
If the GPH of the filter is not sufficient for the size of the tank and its surroundings, “dead spots” can form. Dead spots are pockets of water that are not stirred by the action of the water current and usually form if the GPH provided by the filter unit is not powerful enough to circulate all the water in the aquarium equally.
The water in these dead spots is stale and stagnant, providing the perfect environment for harmful bacteria that can cause health problems for your fish.
Dead spots are the main reason I suggest you use a filter that has a higher GPH than the tank capacity warrants. That’s because the basic GPH doesn’t take into account the aquascape in the tank. Essentially, the more plants, rocks, driftwood, and other decorations you have, the stronger the water current needs to be to reach all areas of the aquarium.
In large tanks, the best way to combat dead spots is to use two filter units, one at each end of the aquarium, to ensure that water in all areas of the tank circulates through the filter units.
Does Sand Get Trapped In Large Filters?
Under normal operating circumstances, sand will not be absorbed by a large filtration unit. However, problems can arise during routine tank maintenance and sometimes fish sinking into burrows can cause clouds of sand to build up around the tank and eventually end up in the filter unit. Most of the time, the sand in the filter just makes more work for you, since you have to clean the unit more often than you normally would. However, sand can sometimes damage the filter.
If sand is not cleaned out of the filter, it can clog the unit, which means fish debris, food scraps, etc. they stay in the tank, where they will break down and release harmful ammonia into the water. The biological media in some systems can become clogged with sand, affecting the efficiency of the bacteria that process the waste and purify the water.
The mechanical element of all filtration systems uses an impeller or motor that draws water through the filter unit and the enclosed media before returning clean, polished water to the tank. If sand is sucked into the impeller, it can damage the moving parts of the filter and prevent the impeller from turning.
When the impeller stops working, the filter no longer draws water from the aquarium. The only solution is to replace the filter unit completely or send it to the manufacturer for repair. This is why many power filter manufacturers recommend using only pebbles, gravel, or glass marbles, rather than sand as a substrate.
Damage to filter parts
Even if the impeller is not affected, the sand can still cause damage to the internals of the filtration unit by wearing down any components that are made of plastic. That can result in the filter not working as efficiently as it should. Small holes can even develop in the filter housing, causing leaks and preventing the unit from working properly.
What To Look For In Aquarium Filters For Large Tanks
Large tanks have their own particular requirements when it comes to choosing the right filtration systems. The type of filter you choose will depend on the configuration of your individual tank. However, there are several general considerations that apply to all hobbyists who maintain large aquariums.
As mentioned earlier in this guide, it is essential that you choose a filter with the right capacity for your fish tank.
Check the GPH on the product packaging and choose a filter that offers a little more capacity than you need for your tank size. If you have a very large tank and plan to use two filters, choose units that have the exact GPH for your aquarium so you don’t create a current that is too powerful for the tank’s residents.
Remember that a heavily decorated and planted tank will be more prone to developing pockets of standing water, especially in the corners. So be sure to keep that in mind when purchasing your filter.
Aquarium filtration has three elements:
Each of these processes is essential to a healthy environment in which your fish can thrive, and it is important that you understand how each element of the filtration process works.
The mechanical element of the filtration system is the process by which particles of fish waste, uneaten food and general debris are removed from the tank. The filter unit has a motor that drives an impeller, drawing water from the aquarium, through the filter media, and back into the tank.
Filter media can be made of foam, pads, dental floss, folds of paper, and diatomaceous earth, and its job is to trap and hold debris particles. The filter media should be cleaned regularly by rinsing it with tank water to remove excess particles before it turns into sludge and clogs the filter. If you don’t clean the filter media, the mechanical filter will eventually become blocked and the water flow will decrease.
If you don’t clean the mechanical filter at least once a month, it will end up retaining large amounts of decaying matter that will slowly overload the biological filter and contaminate the water.
The system’s chemical filtration element is designed to remove toxins, heavy metals, and chemicals from the water as it passes over some type of resin or chemical media. Traditionally, activated carbon was the preferred chemical filtration media, but now you can buy specially targeted products that remove specific substances from your water.
You can incorporate these media into your filtration system as a way to reduce the amount of maintenance you need to do and to improve water quality. That said, you should still do partial weekly water changes to keep nitrate levels to a minimum.
Chemical filtration media generally need to be replaced on a regular basis to remain effective. Also, some fish disease treatments are removed by chemical filtration media, so you’ll need to remove that part of the filtration system while the fish are undergoing treatment. Alternatively, remove the fish and treat them in a dedicated hospital tank with a filtration system that lacks the chemical element.
Biological filtration uses several different species of bacteria to process the toxic chemical byproducts that are created by breaking down fish waste, food scraps, plant debris, and general detritus in a process called the nitrogen cycle.
In the first part of the nitrogen cycle, ammonia is produced.Ammonia is highly toxic to all aquarium inhabitants and can be fatal to your fish if levels of the chemical are too high. In the next part of the nitrogen cycle, Nitrosomonas bacteria break down ammonia into nitrites.Nitrites are also harmful to aquarium life if not removed. Nitrites are consumed by another type of bacteria called Nitrobacter and are converted into nitrates.
Nitrates are much less harmful to fish and invertebrates than ammonia and nitrites, but if they are allowed to accumulate in water, high levels can trigger algal blooms. Therefore, partial weekly water changes are required to remove nitrates, ideally at levels of less than 20 ppm (parts per million).
The bacteria that drive the nitrogen cycle need oxygen to survive, as well as a place where they can form colonies. The biological element of a filter system consists of a filter medium within the unit in which bacteria can grow. Due to the bacteria’s need for oxygen, the most efficient biological filters are those in which the biological media is exposed to air.
There are many different types of filters, but the best designs to use for very large tanks are cartridge and power filters.
Power filters come in different designs, but these units are basically designed to hang on the back of the tank. Most power filters use all three types of filtration and are extremely efficient and easy to maintain. Power filters come as complete units with an integral pump and filter cartridges, requiring regular cleaning and replacement to remain effective. All three filtration stages are contained within the filter unit.
Many modern power filters come with bio wheels. A biological wheel is a biological filter formed by a wheel of pleated material. The wheel turns as the water passes over it by the pump, providing the bacteria colonies on the surface with a good supply of oxygen.
Power filters are not the best choice for a heavily planted aquarium as they cause too much surface agitation that is not compatible with a CO2 injection system. Also, when used on a saltwater tank, a power filter can cause salt to seep into the underside of the tank hood and into the light unit. Also, fish species that are not good swimmers can become stressed if the flow in the tank is too strong, so a power filter may not be the best option in that case.
Canister filters usually live under the tank in the cabinet. These are pressurized units that perform all three types of filtration. Canister filters come as a complete unit with an integral pump or in a modular form requiring a separate pump. Modular units can be useful as they offer the versatility to be combined with another form of filtration, such as a wet-dry unit.
Canister filters typically have a u-tube to bring the water into the unit and a spray bar to return the water to the tank. Once you start the system, the water is drawn from the aquarium into the canister filter unit, where it passes through several chambers containing filter media before returning to the tank.
Canister filters are powerful and super efficient, making them a great option for a very large aquarium.
Regardless of the type of filter system you use, some maintenance will need to be done to keep things running efficiently and effectively.
If the filter system contains cartridges that hold the media, they will need to be replaced periodically and the cartridges will need to be flushed with tank water each month to remove sludge that would otherwise clog the unit.
To ensure that the impeller is free and able to rotate without obstruction, you should make it a part of your cleaning routine to check for debris trapped in the impeller housing and clean as necessary.
When choosing a filter for a large tank, there are a few practical considerations to keep in mind:
Your first consideration should be the amount of space you have both inside and outside of the tank. If you have a very large aquarium that sits in a location without much space around it, you don’t want a HOB (hang-on-back) filter that is inconvenient to access for maintenance. So a canister filter that fits under your tank would be the best option.
You want to enjoy watching the tank residents and their aquascaping efforts, not the sight of a huge black filter box, especially if you need two filter units to manage the environment efficiently.
If that’s the case, you need some kind of external filter system that won’t mess with your eyes.
Ease of maintenance
If you have a busy lifestyle, you may not have time to spend hours cleaning a complex filter unit. If that’s the case, choose a system that’s quick and easy to maintain.
The 5 Best Aquarium Filters For Large Tanks
Now that you know more about which filter to choose for a large tank, let’s take a look at five of our favorite products that fit the bill.
1. fluval 406 external filter
- 100 gallons
- 9.5″ long x 17.25″ tall x 7″ wide
- 400 GPH
fluval is a well-established company whose products are generally of very good quality and very reliable.
The fluval 406 external filter comes with an instruction manual and is easy to set up. Thanks to automatic priming, it’s simple and seamless to get water flowing through the filter, and the noise reduction technology that has been used in the design ensures that the pump is much quieter than many of the product’s competitors.. Unit maintenance is a breeze with removable filter baskets and easy-lift brackets.
The only real drawbacks to the filter unit are that it doesn’t include a lot of filter media or length of hose.
- well made and durable
- Extremely quiet operation
- Could come with more filter media and hose
2.Eheim Pro 4
- 75 gallons
- 10″ long x 10″ wide x 14″ high
I use Eheim filters on both of my tanks and love their simple, easy-to-clean design and reliability.
This external canister filter has a pump button to start the siphoning process, and you can adjust the flow from zero to full, which is a useful feature if you have fish that don’t appreciate a lot of flow through the tank. The media trays are designed so you can lift them individually for cleaning, and each tray has a triangular marker in one corner to make sure you align them correctly when replacing them in the drive.
There is a release button to disconnect the inlet and outlet valve block from the unit for cleaning, making the process simple and quick to accomplish.
- User friendly design
- Extremely quiet operation
- Flow can be variable
- Not robust construction
3. Fluval Canister Filter, FX6 Filter
- 400 gallons
- 10″ long x 10″ wide x 21″ high
- 1600 GPH
If you’re looking for a 400 gallon aquarium filter, the Fluval FX6 External Canister Filter might be just what you need.
The unit has an expandable inlet tube that allows you to adjust the filter to fit most tank sizes and shapes. The pump is self-priming; just plug it in and go. There is a special air evacuation function that removes air bubbles from the system every 12 hours so maximum vacuum is always maintained.
The system uses mechanical, biological, and chemical filtration, and the unit comes pre-loaded with a full set of filter media that can be interchanged and customized to fit your setup. The purge valve system simplifies maintenance and the multi-directional outlet nozzle allows you to direct the flow of water to suit your fish’s preferences.
- User friendly design
- Customizable filter media
- Sponge filter media needs frequent replacement
- bulky design
4. aquaclear CycleGuard power filter
- 110 gallons
- 7.1″ long x 13.9″ wide x 9.1″ high
- 400 GPH
The aquaclear CycleGuard Power Filter is a HOB unit that uses multi-stage filtration to maintain excellent water quality in large tanks. The system incorporates mechanical, biological, and chemical filtration using disposable filter cartridges, and you get a complete set of filter media with the system to get you started.
This filtration system features a gentle waterfall design that returns clean water to the tank without creating excessive surface agitation, making it a great choice for fish and plants that don’t appreciate a strong current in their habitat. The design also ensures good oxygenation of the water.
- Smooth waterfall return design
- Filter media included
- Three stage filtration
- Filter cartridges are expensive to replace
5. Penn Plax Cascade 1500 Elite Aquarium Filter
- 200 gallons
- 11.5″ x 20.5″ x 12″
The Penn-Plax External Canister Filter is one of the best 200 gallon fish tank filter systems out there. The unit comes complete with everything you need to connect it to your aquarium. Start-up is via a push-button primer, and the unit has fully adjustable 360-degree swivel valve taps so you can alter and redirect the flow to suit your setup.
The filter system comes with large filter pans, inlet/outlet tubes, and filter media to get you started, though you can customize the media you use to suit your needs. Extra-large filter pans mean you can use more filter media that requires less frequent replacement. The pump is super quiet and efficient.
- Extra Large Filter Media Pans
- Customizable filtering
- Fully adjustable flow
- Too much water bypasses around the filter compartments
We hope you have found this guide and the product reviews helpful.
Of the products we reviewed, our favorite is the aquaclear CycleGuard power filter. This product is powerful enough to keep a large tank clean, but the gentle return of the waterfall means fish and plants won’t be hit by a strong flow. The three-stage filtration system gives you everything you need to give your fish a pristine environment in which to thrive.
Also, the HOB design of this high-quality external filter is ideal for you if you don’t want a nasty unit in your tank but don’t have an aquarium cabinet to hide a canister filter system in.