Can an Aquarium Filter Be Too Big or Too Strong?

One of the most vital parts of any aquarium setup is the filter. While new tank owners, may purchase all-in-one solutions that come with a tank and a filter. There are occasions where either the filter dies, or they upgrade the size of their tank. It is common sense that a new filter that is too small won’t do a tank any good, yet it can leave tank owners wondering.

Can an aquarium filter be too big or too strong? Physical size isn’t so much the issue here, although if it is too large, it may not fit on your tank. The answer to filters being too strong is yes. The generated flow of water causes more issues than lots of filtration. There are fish that don’t like strong water currents, and if they are too small, they can find themselves sucked toward the water inlet.

Keep reading to learn why you ought to tailor your aquarium filter to match the size of your aquarium. You will also see why bigger and stronger isn’t the best solution, and what you can do to resolve the issue if you already have a large filter in place.

What Size Should My Filter Be?

To look at the effects of large filters have on your tank, it is advisable to understand what size the filter ought to be. The consensus is that the volume of water in your tank (number of gallons) should pass through the filter four times every hour.

If your filter can do more than this, that isn’t the issue. You should always be sure your filter matches your tank, or it can move the tank volume more than the minimum number of gallons per hour.

A quick example being if you have a tank of fifty gallons. This requires 200 gallons per hour as a minimum. If you have a choice of 180 GPH or 220 GPH, then you will be better to choose the 220 GPH filter.

How Will I Know the Water Flow is Too Fast?

One of the benefits of fast-flowing water is agitation and the adding of oxygen. Many tank owners think if they see bubbles, then all is good in their tank. However, once this flow begins to hamper the natural swimming rhythms of your fish, then there will be problems for several reasons.

Here are a handful of the common signs your water flow is too strong.

  • Fish struggle to move at their own pace
  • Larger finned fish show retarded rates and more dangling motions
  • Smaller fish such as Betta struggle to swim at an angle and swim in a different manner than usual
  • Several kinds of fish take to hiding rather than swimming around the tank
  • Some fish find it hard to maintain their balance as they swim

These symptoms are basic for a fast current. However, if the water is excessively forceful, then you can face more harmful issues. Fish can find it hard to feed; this is true for floating fish or the slow movers. They won’t possess enough energy to follow their food through a current.

Fish can become malnourished as a result, and you will find more food is breaking up and affecting water because it isn’t eaten.

Benefits of a Good Filter Flow Rate

If the flow rate isn’t too strong, then you won’t over filter your aquarium. Even when using a larger filter, it is not possible to over-clean your water. You can, though, push the water through the filter too fast, which will affect the impact of your beneficial bacteria.

Here are a few benefits of good water flow through your filter:

  • Increased oxygen levels: Filter pumps, especially those with the cascade feature, disrupt the surface of the water and allow more oxygen to dissolve into it, thus making it easier for fish to breathe.
  • Better waste removal: One of the most important tasks of the filter in the tank is to clean the dirty water and remove the waste. Filters with adequate water flow will be efficient in doing this.
  • More natural environments: No species of fish lives in stagnant waters, so it is vital to have a current that matches the natural habitat of each of your fish. The closer you are to mirroring their natural habitat in your tank, the happier your fish will be.
  • Improved water circulation. Ensuring water stays in motion in your tank helps avoid dead water zones, which are great breeding grounds for anaerobic bacteria and other microorganisms, which can cause problems in your tank.

Water Needs Contact Time in the Filter
If you have a larger than the necessary sized filter, but have water flow that is suitable for your tank, then you won’t have a problem. You can’t over clean a tank. Once your water flows through your filters, the toxins and other harmful things are removed from the water by the beneficial bacteria. These accumulate around your filter inlet.

You find that if the filter is too powerful for the tank size and the water passes through too fast, and the water won’t have enough contact time with these beneficial bacteria.  The fast-moving flows stir and move the tank contents, but don’t uniformly distribute whatever is necessary to sustain less aggressive aquatic life.

The beneficial bacteria, the oxygen, and the warm water temperatures only partially circulate the tank. Inhabitants of your tank find a full dividend in the areas where they swim.

Ways to Adjust Filter Strength

Any tank owner who has concerns over their filter should choose the more powerful option. However, before doing so, you will need to check the filter has one thing added. This can make all the difference to the survival of your fish without worrying about the size or strength of your filter pump.

Here are a few ways you can reduce a strong current from your filter and make it more suitable for your fish and the aquatic environment.

  • Buy a filter with adjustable flow control: Many filters come equipped with flow control valves. It is easy to adjust these to reduce the flow of water that passes through the filter. You can find the same on pumps where you are using these separate to your filter. This will allow you to have the most water contact time with the filter media.
  • Baffle water intakes. Although not usually a recommendation as this can overwork your pump, you can baffle the water inlet with a sponge. This reduces the flow of water that can enter your filter.
  • Plant and rock placement. You can reduce the current by placing a bunch of live plants in line with your filter inlet. While this doesn’t decrease the amount of water that passes through tour filter, it can be enough to break the current to allow your fish lots of area to swim without issue.

A rock-scape can also make great water breaks and function in the same way. Both of these options leave the far end of your tank for smaller fish to reside in as if they were in a natural habitat.


As you can see from all the above, you can’t have water which is too clean for your fish. However, it is the means of obtaining this clean water, which can pose problems. As long as you have a pump or filter where you can regulate the flow, then you have plenty of scope for upgrading your tank without the need to purchase another pump.

In the meanwhile, be sure you adjust the flow so your fish can swim naturally without exhausting themselves fighting against the flow.

Related Questions

Why do my fish want to swim closer to my filter? There are a few reasons fish tend to swim closer to filters. Fish know that faster waters mean more oxygen. This means they know they can breathe better in those areas. Secondly, you can find many fish are opportunistic when it comes to feeding. Rather than wait for food to come to them, they hang around the filter where they know the food will go in the current.

When is my filter too large for my Betta? You find this is more to do with tank size in relation to your Betta fish. Betta are happy to live in the smallest of places without issue, and means they can survive in smaller tanks or bowls in the same manner as Goldfish can do. If your tank is on the smaller side and isn’t above two and a half gallons, then you will need to avoid using a filter. Currents here are unavoidable, and it will stress your fish into becoming ill.