My Aquarium Filter Has Stopped Working! What Should I Do?

A fishkeeper friend recently messaged me in a panic. She was worried if her oscars were going to die while her filter was offline; she was waiting a couple of days to get a replacement part to fix her filter.  So, she posted her question in a Facebook group. She received some alarming answers. I, however, assured her that her fish would probably be fine as long as she took some extra measures in the meanwhile.

Messy eaters like oscars really need a working filter
Messy eaters like oscars really need a working filter. Check out this article on lutino oscar cichlids.
Credit: By Ashish Ghosh, CC BY-SA 3.0
So, What Should Be Your First Concern When Your Filter Breaks Down?

Aeration, aeration, aeration.

If your filter was the only source of surface agitation, then oxygen won’t be getting into the water at the rate your fish need it.  Solution: grab an air pump (reasonably priced, widely available) and put an airline into your tank as soon as you can.

sponge filter
Aquarium sponge filters don’t have mechanical parts and therefore are less prone to “breaking down”.

From time-to-time, you might find yourself unable to obtain an air pump–or maybe your power’s out.  Therefore, in these cases, I recommend something more rudimentary: manual agitation of the water. Manually agitating the water can be exhausting, but will worthwhile if your tank is heavily stocked.

You have a couple of options when it comes to manual agitation.  My preference is to simply use a plastic cup to scoop water out and pour it back in at regular intervals.  Another method is to grab a straw and blow air into the water.  The latter can leave you lightheaded, so take care with that one.

Now Your Fish Have The Oxygen They Need – What Next?

Large, regular water changes will be the key to maintaining the health of your fish in the absence of adequate filtration.

As you may already know, your filter is home to a healthy colony of bacteria that processes ammonia into nitrite and then nitrate.  Ammonia is bad.  Nitrite is bad, but less bad.  Nitrate is kinda bad in high concentrations.  Your filter efficiently moves the tank water through this colony of bacteria, thereby “cleaning” the water.

Without a working filter, the nitrogen cycle will slow down significantly in your aquarium.
Without a working filter, the nitrogen cycle will slow down significantly in your aquarium. It can be dangerous to overstock your aquarium – check out this article on the topic.

So, without your aquarium’s water constantly passing through your filter damaging amounts of ammonia will build up in your tank.

Changing your water will solve this immediately.


But, while your filtration system remains absent, ammonia will simply build up again after the water change.

Ammonia Has Quickly Built Up Again. What Should I Do?

You guessed it… change the water again! So, keep water conditioner in stock—grab it at Amazon.

The ammonia chemical compound is bad for your fish.
The ammonia chemical compound is bad for your fish.

I say, change around 50% water everyday. Although, this is an overly cautious best guess. Every aquarium is stocked differently; therefore, it’s impossible to offer “one size fits all” advice.

Ammonia Sounds Pretty Bad. Can I Do Something Else To Keep It Down?

Yes, in addition to water changes you should stop feeding your fish. If they don’t eat, they don’t produce as much waste.  It’s very, very simple.  It can be a bit emotional to watch your fish go hungry, but they are certainly very capable of going a couple of days without food–don’t worry.