Should an Aquarium Filter Be on All the Time?

When new tank owners begin setting up their systems, there are a couple of things; they may not understand. They make all the investment and research as much as they can about their fish; they know what food and what the water levels are to be for the pH and everything else.

It comes to the day when they begin adding their fish to their tank, and then they have a thought about one component of their aquarium.

Should an aquarium filter be on all the time?  The answer to this is yes; aquarium filters need running around the clock for as long as you are keeping fish. Depending on where the tank sits, it can appear noisy at night, and tank owners want some peace. However, turning a filter off for a period of eight hours could be the end of your fish.

Now, we will look at all you need to know about filters, and what happens in your tank when using one.

Filter Functions

Before you think about having fish, you ought to understand what your filters will be doing as they run in your tank. While learning this, you can see why it is better never to turn your filter off for extended periods.

The following three areas will be dependent on the type of filter you use; however, these are three areas taken care of by aquarium filters one way or another.

  • Mechanical filtration: This is brute force in effect and the first in the line of any part of your filter. Debris and waste will hit the first part, and not pass any further. This helps keep the tank clean and the water aerated as it circulates.
  • Biological filtration: When fish breathe and pass water through their gills, they produce ammonia. Besides, any waste they produce also produces ammonia as it breaks down and sinks to the bottom of the tank. A filter system will remove this ammonia as water passes through it, and delivers safe clean water back to the fish.
  • Chemical filtration: Water isn’t as pure as it appears, and some chemicals can harm fish. Chlorine, copper, among others. Some of the larger filters have the capability of removing these toxic compounds from the water.

Different Types of Aquarium Filters

Now you see the three areas filters deal with. You need to understand the kinds of filters you can choose. There are many types of filters; however, here are three of the most common powered filters you can find.

Power Filters: There is a broad price range that covers filters in this bracket. Most are easy to use and cover the basic requirements for your tank. Most models come with a replaceable filter or a bio-wheel, which delivers additional support in the biological department for your tank.

Canister Filters: if you have a large tank, then canister filters are the kind you usually use. They do offer plenty of filtration, yet they do require a little more care and maintenance.

Undergravel Filters: You can find these are a little different from many other filters. You place these underneath gravel layers, and they work by using air pumps or powerheads. This variety of filter excels as a biological filter, although there are several which include replaceable filters as well. By doing so, they can also deliver mechanical or chemical filtration.

Water Filters and Air Pumps

If you are wondering whether you can turn off your filter during the night. There are things you need to consider.

Fish get their oxygen from the water as they pass this through their gills. Once you turn off your filter, unless you have a separate air pump, then this oxygen will deplete. Additionally, warm water can’t hold as much oxygen as cool water, thus the warmer your tank, the lower is the capability of retaining oxygen.

Here are the different scenarios of when you have separate air pumps or integrated pumps in your filter. You will see what you can turn off and what you can’t.

Separate filter and air pump: if you have an additional air pump in your tank and it isn’t connected to your filter, then you can turn this off during the night. Air pumps usually sit outside the tank and can make more noise than your filter.

As long as your water filter continues to run, there should be sufficient dissolved oxygen in your tank until your air pump begins again. You will need to be sure your filter is the right size for your tank and not receiving support from your air filter.

The actual process of filtration and water passing through the media and pumping back into your tank ought to be sufficient to deliver enough oxygen for a few hours.

The reason why your filter needs to run all the time, even if you turn off your air pump is to keep the nitrate and ammonia levels in check.

Integrated air pumps and filters: Some of the more affordable units may be all in ones. If this is the case, then there is no way to turn off the air pump without shutting off the filter. We saw your filter needs to run around the clock.

It isn’t possible to turn off your filter for eight hours per day because the ammonia and nitrites will rise to toxic levels.

If you have a separate air pump, and you think turning this off overnight can be an option, this has some factors that need consideration before you do so.

Fish tank size: Aside from the size of your tank, you need to look at the number of fish you have, and the size of them in relation to your tank size. The larger the number of fish, the more fish are sucking oxygen from the water. If you have a large tank with not so many fish, then it may be safe to turn off your air pump if you are on the borderline maximum for fish to your tank size. It may be a fine line they can deplete all the oxygen from the water during this period.

Aquarium plants: Once you look at this area, some tank owners make a simple mistake. Aquarium plants do as other plants do, and partake in some photosynthesis during daylight hours. What isn’t well known is plants do the opposite during dark periods. In the case of the aquarium plants, during dark periods, they will suck oxygen from the water.

Once they do this, it can affect the dissolved oxygen for your fish. Thus, the more plants you have, the more oxygen they will consume overnight. No tank owner wants to wake up to find they have dead fish, yet they have healthy plants.

Water agitation and filters: Filters make all the difference, as does the type of filter you are using, and how much water agitation it creates. Filters like the undergravel filter, or one you submerge will not produce any dissolved oxygen. Filters that are like mini waterfalls and hang on the back of your tank produce much more oxygen as they break the surface of the water.

HOB (Hang on Back) Filters are great ways of adding oxygen to the water. You can find the sound of rippling water soothing most of the time. Many of these aquarium power filters do dampen sound.


You may want to turn your filter off at night or wonder if you can turn it off to conserve electricity. However, once you have your aquarium, you do need to be prepared to leave your filter running all the time.

It is part of having an aquarium, unfortunately, yet as we saw, depending on the filter you have, you may have an additional air pump you can turn off for a few hours per day with no ill consequences. If you have concerns, either you may not have sufficient oxygen, from an air pump, or your filter isn’t working, as it should. You can purchase dissolved oxygen test kits.

This can be a quick way to find if your fish lack oxygen or they have enough. While you may not be able to switch off your filter, you can always check out a quieter filter and use that.

The main aim of a filter is to keep the ammonia and nitrite levels low, and unfortunately, there isn’t any other way you can do this on your indoor aquarium.

Filters are cost-efficient, and the noise is far from overbearing. Therefore, you can do as many aquarium owners do, and relax to the sounds of babbling water.