Why Fish Tank Filter Running Slow? (Reasons and Fix)

The filter is one of the most important pieces of equipment in a fish tank. It maintains the underwater environment and ecosystem for fish. It is not uncommon to have a problematic filter.

Most of the time you can fix it by adjusting the flow rate adjustments. If the setting is fixed on a slow mode, your aquarium filter will also run slow.

But there are some other reasons as well. Read this article to know what you can do before replacing the filter.

Why Fish Tank Filter Running Slow
Fish Tank Filter

Why Proper Filter Flow Rate is Important?

If the water flow rate is not appropriate according to the fish living inside it, you will never be going to see or enjoy its true potential.

Some fish needs a high flow rate to thrive, and some needs low. It actually depends on what that fish is and where did it come from. Then recreating their natural habitat as much as possible.

Another reason that it is so important – if the filter flow rate is too slow, the water will not get filtered as it needs to be. As a result, the water, filter, plant basically all the things inside the fish tank will be dirty and eventually toxic.

It is very dangerous for the living being inside it.

Why My Fish Tank Filter is Running Slow? Reason and Fix

There are some common reasons you need to look for if your filter is getting slow. Do not go for the replacement first thing. Look if you can find any of these problems in your filter.

The Filter is clogged

A clogged filter is one of the main reasons it is getting slow. Over time dirt and debris build up inside the filter and clog various parts of it – especially the biological filtration system. If it gets fully clogged, it is almost impossible to get water past through it.

The Fix

The solution to this problem is to clean it thoroughly. Unplug the filter and take it out from the fish tank. Especially look for any clogged area that can slow down the filtration process and clean it.

While cleaning a filter you need to keep in mind that you cannot clean it 100%. If you do so, all the good bacteria will be gone and it will be harmful to the aquarium ecosystem.

Another thing is, you have to clean the filter with old tank water. Tap water also kills those good bacteria.

The Impeller is Broken

A broken impeller may be another reason why your filter is slowing down. Because if the impeller is the problem, it slows down the water pump as well. Then the water pump cannot pump the right amount of water which causes slow water flow.

The Fix

Do not worry, you do not have to change the whole filter if the impeller is broken or troubling. Firstly, unplug the filter and unassembled it to see if the impeller is alright.

The problematic impeller has to lot of dirt around it. Clean it as mentioned above and see if anything improves. If not and you are sure it is broken, only replace the impeller and it will do the job.

The Hoses are Dirty

The hose pipe included with the filter tends to get dirty sometimes which directly affects the water flow inside the tank. Because water cannot flows through the pipe as it should. As a result, the filter runs slow.

The Fix

To see if it is the problem or not, you need to unplug the filter first and take it out. Then separate the hoses from the filter.

Take a bucket of warm water and soak the hoses for 30 minutes. By this time the dirt will loosen up and it will be easier to clean.

Use a hose cleaner brush to properly deep clean it.

Improper Flow Rate

Many filters come with an adjustable flow rate. If there is a problem while setting the adjustments, the filter can run slow. Such as, the setting may be lower than it needs to be.

The Fix

This is a simple fix. You just need to know the settings properly and learn how to adjust the flow rate in that particular filter. Then just fix the setting and you are good to go.

What Kind of Fish Tank Needs Slower Flow Rate?

If the tank consists of betta fish, baby fish, small fish, or live plants it will need a slow flow rate. Otherwise, it will create unnecessary stress for those fish.

Of course, there are exceptions but, in most cases, those delicate fish need a slow flow rate. they cannot adjust to the high flow rate because it does not match their natural habitat.

The first rule to make the fish comfortable inside the aquarium is that, recreate the natural habitat as much as possible.

When do You need to Change the Filter?

If you have tried all of the methods mentioned above and none of them worked, you need to replace the filter as soon as possible.

The most common reason for the filter not working at its full potential is mostly the dirt. A dirty filter creates a lot of problems. It also goes away with proper cleaning.

If you clean and maintain a filter on regular basis, it will not create most of the common filter problems. But if it does not work and you can find that the impeller or the motor is fully broken and cannot be repaired, you need to change the filter.

Frequently Asked Questions (FAQs)

How do I increase the flow of my aquarium filter?

You can add an air pump and some air stones to the aquarium.

How do You Know if Water Current is Too Strong?

In this case, the fish will not swim and hide constantly. It will make them stressed out.

Is it OK to use 2 filters in a fish tank?

Yes, if your fish tank is big and the current one cannot clean it properly, you can add another filter to the tank.

How long can you leave a fish tank filter off?

You should not turn off the aquarium filter. If it is an emergency, you can turn it off for ½ day.


A filter will not be perfect all the time and fish tank filters are prone to have problems often. Do not panic right away. See if it is something you can fix.

If repairing is not possible, replace it. You can take up to 3 to 5 days but do not prolong the replacement more. Because your fish will start to suffocate in the tank and in the worst case will die.

Related Posts:

Arif H Fahim

Welcome to PetFishTank! My name is Arif. I make an effort to publish educational articles using my many years of expertise as a fish owner.

Recent Posts