Can You Have Multiple Aquarium Filters in One Fish Tank?

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Every aquarist tries to build up the perfect aquatic setup for the fish. There are a lot of aspects to cater to in this sense, filtration being one of the most important.

Not all fish require the same filtering power, and the same goes for the environment as a whole. We will discuss this aspect in due time.

So, how do you know whether using one filtration system is enough, or you need 2 filters to get the job done? Let’s see!

What is Redundant Filtration?

Redundant filtration refers to using 2 different filters for the same tank.

This can happen for reasons like:

  • The tank is too large – Many aquarists consider redundant filtration for aquariums larger than 100 gallons. It’s true that you can have one filtering system for the entire 100-gallon water volume, but that may come with some downsides. For instance, the filter may need to produce faster currents to keep up with the entire water volume. This may damage plants and cause discomfort to aquatic life. Redundant filtration will avoid these issues.
  • The fish are too messy – This can happen at times. Cichlids are infamous for producing a lot of waste and fouling their environment fast. A large 100-150-gallon cichlid tank will most likely require redundant filtration to cope with the fish’s waste-producing capabilities. There are ways to avoid that, but you will need to compensate for it via more thorough manual tank maintenance and cleaning.
  • Overcrowded tanks – If the tank is overcrowded, the resulted fish waste and food residues may overwhelm the filtration system. Having 2 filters will solve that problem. Or at least diminish its impact.

An important note here. Redundant filtration is only scalable in relation to your tank’s water volume instead of the number of fish. To put it more simply, you could use 2 filters ranked for 50 gallons for a 100-gallon tank.

This would be the optimal redundant filtration. However, using 2 75-gallon ranks filters for the same amount of water won’t provide any extra benefits.

The latter won’t allow you to add as many fish as you would add to a 150-gallon tank just because you have 2 75-gallon filters. It doesn’t work like that.

Now that you know what redundant filtration is let’s check its benefits and downsides to see when to use it and if it’s worth it.

Benefits of Using Multiple Aquarium Filters

I would say there are several fundamental benefits to relying on redundant filtration to stabilize and clean your tank.

These include:

  • Prevent blackouts – Some filters will clog over time, especially if you don’t have the strictest maintenance routine. This can also happen due to the filter sucking in larger particles like gravel, poop coming from larger fish, plant residues, etc. It’s useful to have another filtration system in place to keep the system stable until you unclog the faulty one.
  • Boost biological filtration – Biological filtration refers to allowing nitrifying bacteria to settle in the environment and take over the task of turning ammonia into nitrates. These microorganisms exist in every aquatic setup, whether it’s close or open. Without them, the system would become uninhabitable since ammonia and nitrites are poison to most aquatic life. The nitrifying bacteria will form colonies inside the filtration system but will also spread throughout the tank, especially among rocks and in the substrate. Having 2 filters in place may be necessary in case one filter cannot handle the system’s waste load due to the excessive water volume. This way, you will have 2 filters for twice the number of beneficial bacteria working to maintain the system’s stability and combat ammonia and other harmful chemicals.
  • Prevent strong currents – The more water volume the filter is required to handle, the stronger the currents it will produce. A 50-gallon filter won’t be able to manage a 100-gallon tank without producing excessive currents that may not be in your fish’s best interest. Some species hate fast-flowing waters as it causes them discomfort. In that case, having 2 filters will mitigate the problem since each system can handle half the tank.
  • Easier cleaning, less biological risks – You should have a clear filter cleaning routine to ensure the system continues to operate at maximum capacity. Filters require cleaning mostly once every 4-6-8 weeks, depending on the filter’s size, the tank size, and the type of fish you have. Having 2 filters will allow you to clean one while still keeping the tank’s filtration somewhat active during the maintenance work. You will also protect the filters’ biological film better. That’s because, when cleaning the filter, you will inevitably kill some of the beneficial bacteria inhabiting it. Fortunately, you have the other filter’s biofilm intact, which can restore the other filter’s biofilm shortly. So, cleaning the filters one by one, several weeks apart will preserve the tank’s biofilm more effectively.
  • Complementary filtration effects – Not all filters are designed to provide the same type of filtration. Some are specialized in biological and mechanical filtration but cannot offer chemical filtration. Many people solve this issue by relying on 2 filters, each with its own benefits.

There are also some downsides to consider since having 2 filters isn’t always the ideal move.

Drawbacks of Using Multiple Aquarium Filters

The most noticeable downfalls of using more than one filter per tank include:

  • Too powerful currents – This problem is generally linked to positioning. Some aquarists will place the filters on the same side of the aquarium. They do this either due to not realizing the effects or because of the tank’s placement. Either way, the result is doubling the water currents from one side of the tank and disrupting the aquatic life in the process.
  • Destroying the plants – Heavily planted aquariums shouldn’t have more than 1 filter. Otherwise, the boost in water flow can hurt the plants, especially more sensitive species that require calmer waters.
  • Stressing the fish – Some fish love faster-moving water currents, especially those living in rivers. However, other fish hate fast-moving waters, which is why you will often see them staying clear of the filter’s area. That’s possible in a tank with one filter, but it’s nearly impossible in one with 2 systems. Since your fish won’t have a safe space to retreat to, it will be constantly subjected to the higher currents and become stressed as a result. As you know, fish experiencing prolonged stress will eventually showcase weaker immune systems and face diseases and infections more often than not.
  • Taking up too much space – This can be an issue when using 2 filters for fish that are known to be more energetic and territorial. These tend to require more open space, as well as a well-crafted tank layout consisting of plants, rocks, and various decorations. Adding 2 filters to the mix may take up valuable space that your fish could use to their benefit.
  • Circumstantial at best – The idea is that you shouldn’t begin with the idea that you need 2 filters. Or that 2 filters offer double the filtration power, which means they’re always better than 1 filter. The problem is that they don’t scale like that. If you have a 75-gallon tank with a 75-gallon filter already installed, there’s no point in getting another filter. The filter you have installed already gets the job done. Any additional piece will be redundant.

All these pros and cons only show one thing – there is no right answer. Whether you need 1 or 2 filters depends entirely on your situation and needs.

Is It OK to Over Filter Your Aquarium?

Sometimes it is, other times, it’s not. It depends on your situation. We’ve already detailed some of the pros and cons of having 2 filters, and the main downsides boil down to one overarching issue – water flow.

Having 2 filters will almost always produce too powerful water flow, no matter how you do it.

The result may be destroying environmental plants, blowing away the substrate and decorations, and stressing the fish. In some cases, the strong water flow may even make it impossible for some species to breed.

Bubble nesters like the Gourami like to cover their eggs in a bubbly foam, floating at the water’s surface. The filters’ activity can blow up the nests, spreading the eggs all over the tank, where the fish will eat them.

So, always carefully consider the pros and cons before investing in an additional filtering system.

Can You Add a New Filter to an Established Tank?

Yes, you can add an additional filter to a cycled tank if you need to. Many aquarists do this either when adding more fish or when reforming the entire aquatic life altogether.

In the latter case, the newcomers have different environmental preferences, with faster-moving waters being one of them.

In those cases, the additional filter may have its benefits, provided the tank is large enough for that. I wouldn’t recommend 2 filters for a small tank, below 50 gallons, since you get nothing meaningful out of that. Plus, the water flow will be too strong for such a small environment anyway.


Not all tanks will benefit from a dual filtration system. Make sure you need the extra filtration power and, more importantly, make sure the 2 filters complement each other.

If one lacks chemical filtration, ensure the other piece has it.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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