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Not Killing Your Fish Guide | Can I Turn My Filter Off At Night?

Updated on October 14, 2009
Was your filter designed by this guy?
Was your filter designed by this guy?

You know what's useless? Common knowledge. The sort of knowledge that makes claims, but never supports them. Aquarium filters can be loud, even if you buy a good one, and some people just want to be able to turn the filter off at night.

Now the common response to the 'My filter is too loud and my boyfriend is going to murder all the fish if they keep him awake for one more night,' dilemma is to say 'Get him some ear plugs,' or 'Buy a better filter'. Both of those options are viable, and if your filter is unsuited for your tank, then sure, you might be better off buying a new filter.

Then again, you might like your filter. You might have spent good money on it. You might not want to buy an endless stream of filters hoping that one will be quiet enough not to disturb your night's sleep. In this case, your desire to turn the filter off at night may very well overwhelm your desire to keep your fish 100% healthy.

The problem with turning off the filter isn't that the ammonia and wastes will build up to toxic levels overnight, it is rather that (according to some) if you turn your filter off overnight you will kill the bacteria in your filter. Your tank will cycle all over again, ammonia will build up and your fish will die. DIE! (The bacteria in the filter are responsible for converting ammonia into less toxic compounds, but let's face it, if they threaten to die after an 8 hour fast, I don't know how responsible they can really be considered to be.)

In my experience, bacteria are normally more robust than to die if they are not fed for 8 hours. This is assuming you are using an internal filter or a filter that remains saturated in the tank water all night, so they don't dry out and become inert.

In the case of filters which stay wet, bacteria will still be floating in a tank full of ammonia, its just that water won't be drawn past them. Thus, I posit that it should be a okay to turn the filter off overnight. However, unlike other online sources (I'm looking at you, Yahoo Answers,) who simply make statements without evidence, I plan to show my working on this front. It may be that I am wrong, in which case we will all know for sure that you must run your filter all night.

I will be cycling my tank, turning it off from 11pm to 8am, and then leaving the filter to run for the rest of the day. To make things a little more difficult, I am going to be starting a cycle from scratch, meaning my bacteria will not have built up at all when this experiment begins. We'll know if the bacteria die every night, because my tank will never cycle properly if this is the case.

Water will be tested at 8am , before the filter is turned on, and at 10.59 pm, before the filter goes off. If, as people claim, ammonia convering bacteria, (reputed to be Ammonia will simply build up to toxic levels, and because I keep interrupting and killing my bacteria every evening, it will not come down to 0, as it should.

Stay tuned, this experiment will run for an entire month.

(Oh, and fear not, this is a fishless cycle, so no innocent fishies will be harmed in this experiment.)


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      Naomi Gordon 5 months ago

      Do not turn your filter off overnight!!!!! I did... and within 3 nights of doing so... the third night I woke in the middle of the night to find all 3 of My fish were dead!!

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      Natalie blackwood 9 months ago

      I have three tanks at home one community tank guppie mollies tetras my other tank in convicts sharks and barbs i have bubble blower lenght of my big tank and have turned off the internal filter over night still was fine left the heater and bubble blower on tho and they xid fine not sure of i wanted to do it over night every night tho

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      ... 16 months ago

      What are reasult

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      Mat 2 years ago

      In larger tanks you can turn off the filter as long as you have plenty of air flowing through the aquarium. The little treasure chest that bubbles open isn't sufficient. I run my 120gl two filters from 5:30 am till 10:30 pm with 2 single tube aerators on large porous stones and one double tube on a pipe with holes drilled running the length of the tank under the rear rocks running constantly 24/7. Have been doing so for a year and 3 months now and have only lost one fish during a 9 hour power outage.

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      Isabelle 3 years ago

      I also can't sleep at all! But I don't want to kill them! I feel like there is a waterfall in my room!

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      ckb 4 years ago

      I have tested this theory ..and it is safe. I did it to replicate the environment which fish thrive in, drying the dry season there is less running rapids than given in wet season (seasonal), however it will de oxygenate your water. I wouldn't recommend doing this unless you have a "plus "plus size" tank 55 or bigger .

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      isabella 5 years ago

      I actually find the sound of trickling water relaxing

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      Acelaser 6 years ago

      There are tons of ways to work with filters to make to sound less noticeable. The easiest and cheapest is to put a fan, air Puifier or white noise machine between you and the aquarium. Also make sure the water levels in your filter are correct, this will lessen gurgling, bubbling and dripping sounds. Sponges made for aquariums placed strategically in your filter can really help too...

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      lady 7 years ago

      I have a whisper brand and it is not loud but the air pump is making loud bubbles heeelp

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      Becky 7 years ago

      my filter is submerged to about 1/2 an inch and has an arm that has to hang above the water so its the sound of the water running into the tank that keeps me awake rather then the actual filer, it sounds like im sleeping next to niagra falls!! please tell us if we can turn it off at night?? x

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      Anonymous 7 years ago

      ear plugs give me head aches and i don't want to kill my beautiful fish, but i just cant sleep at night, my filter is to expensive to replace and i want to know if i can turn it off at night, pleeeeaaase tell me the results!!! im ready to take a hammer to my fish tank sometimes, it is just sooo loud!!

    • profile image

      tkimoro 7 years ago

      ...uhhh- what happened? Did it work or not?

    • profile image

      Jamie 7 years ago

      @ falalaharaha I second that!!

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      falalaharaha 7 years ago

      please do answer this! my fish's filter gives me insomnia :[

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      newbowl 7 years ago

      I wondered if you ever got a chance to finish this experiment? I have just found this page after reading countless baseless "answers" and I appreciate that you actually want to test it.

    • Hope Alexander profile image

      Hope Alexander 8 years ago

      Unfortunately, I've had a break in this in that the fish tank had to be emptied and moved. This experiment will have to wait for a little bit. Extra information from experts suggests that the bacteria definitely won't die en masse overnight, but deoxygenation may occur and water quality may very well suffer.

      I may have to run this in a separate, smaller tank with a more average filter. I have a power filter on the main tank at the moment and it well over filters the water, so it may not be replicating the results most people would see.

    • Tomgeekery profile image

      Tomgeekery 8 years ago

      I know it's not a month yet, but how's the experiment going?