Can you over filter a fish tank

over filter an aquarium

When setting up your filtration systems in your aquarium you might consider whether it possible to over filter a fish tank. It is something that I have thought about and wanted to find a definitive answer.

With the latest technology in fish tank filtration, you might think that too much filtration is not good for your tank. From what I have researched you cannot really over filter a fish tank. Importantly, you can however under filter. Let us look into the reasons why.

You can’t over filter the water and as such the water can never be too clean. The more filter media you run inside your tank the better the tanks water cycle will be. The result will be that the water is cleaner. Essentially, you can never over filter your tank. The only negative impact would be that the filters cause too much water movement for the size of the tank. This could lead to the residents of your tank being a little stressed out. If you keep delicate angelfish, for example, you need to take care with water movement. The one thing to mention is that you can under filter the tank so more is better in that respect.

Can you use 2 filters in a fish tank?

So we know that you can’t really over filter an aquarium. It is, however, possible to under filter which is why it’s not a bad idea to have two filters in your aquarium, for two reasons. The main reason why lots of reefers have 2 filters is as a fail safe. This is just in case you have a failure in one of your filters. It’s not uncommon for an impeller wheel to fail for various reasons. If this were to happen you know you still have another filter that will still be able to keep up with the bioload.

Again water movement should be considered. As long as the output flow isn’t too overpowering for the fish then two filters will be fine. Multiple filtrations are in fact highly recommended. To avoid output flow being too much for your fish, using a sponge filter alongside a water movement filter. This can reduce overall water movement and can help you keep it under control.

Another benefit to having two filters is that when you need to quickly move fish to another tank. At times when your fish are showing sign of disease, you may need to create a hospital tank. You can quickly use one of the filters from your multiple filtration tank which will already contain good bacteria.

Do i need a filter in a planted tank?

Live plants do some of their own filtering. This is done by the plants absorbing carbon dioxide, which is a byproduct from the fish. This is from the fish exhaling carbon dioxide. If we look at the Nitrogen Cycle we learn that pollutants like ammonia, nitrite, and nitrate will be elements within your tank. Live plants can extract these pollutants and naturally filter out as such. Live plants also keep algae growth under control to a certain extent. This is because they need the same nutrients as algae to grow. As much as live plants do carry out some filtering it would not be advised to allow this to be your only filtration in your aquarium. It is therefore recommended that you install additional filtration to ensure your water remains clean.

can a filter be too big for a fish tank?

On a filtration side, no the filter cannot be too big. Saying that however you also do not want the filter to overpower the space you have either. If you have only got a 20-gallon tank then you do not really need a filter that can filter a 200-gallon aquarium. That would just be complete overkill. It wouldn’t do any harm to the ecosystem. It would absolutely keep your water clean however with the limited space for water flow it might be too much for the size of the tank. Saying that, if the filter does not take up too much room and does not look out of place you can usually lower the current and flow with the adjuster. Many filters now include this feature.

A good rule of thumb is to choose a filter than is at least 10x GPH (gallons per hour) of the tank.

The other benefit if you ​buy an aquarium filter for your fish tank that is significantly larger than you initially need it can be used if you upgrade your tank. This will avoid one of the added costs we face when upgrading equipment. It would almost become an investment to go as large as you can afford early on.

Do I need a filter for my fish tank?

The simple answer is yes. Again, I refer to the Nitrogen cycle which sees fish produce harmful waste (Ammonia). This, unless filtered, will cause harmful diseases in your tank. This can have a significant impact on the longevity of your fish. That said if you had a massive tank with one fish and some live plants then you could get away without a filter. The likelihood of this is rare however this would replicate their natural environment where only natural filters are available to maintain the ecosystem.

In the wild, ecosystems tend to look after themselves. In order that we try and replicate the natural environment in our aquariums, we need the help of filters to accelerate the natural process plants provide in the wild. One way to keep fish without filters is to undertake continual water changes. I would advise against this as this process would be stressful for the residents. Also from a timing perspective, it is not very practical.

The Nitrogen cycle can become quicker by using more than one filter. One thing to remember though is that the parts per million will remain the same as using just one filter. This is because the initial input for the Nitrogen cycle are the waste products in your tank. Unless you have added something which increases the waste then this will remain constant.


Adding fish to your aquarium should not be a problem if you are already running multiple filtration systems. You may be required to upgrade or add filters if your aquarium is at the maximum capacity of fish. The more waste producing items you have in your tank, the more robust your filtration system will need to be. Testing your water for ammonia and nitrates regularly will help you assess the effectiveness of your filters.

One solution to minimizing nasty bacteria is regular water changes. This would be rather than rushing out to buy a new filter. Filters, when set up properly, do all the hard work for us and I personally stick to this.

If your tank is full of fish then water movement becomes a consideration as mentioned earlier. Effective water movement needs additional capacity within your tank. The ability to create effective capacity in your tank for good water movement is reduced if your tank is overstocked. When your tank is overstocked the likelihood of your fish getting caught up in any water movement is higher. For some species this can be very stressful.