Mr. Saltwater Tank

Terrible Advice Tuesday (T.A.Tues): Feeding Your Cat Will Kill Your Fish And Corals

Your cat’s litter box should not be located near your saltwater tank as the ammonia from the litter box (caused by the cat urinating) will get into your tank and raise ammonia levels.

The rest of the story: While your cat might try to eat your fish by catching them, don’t blame Fluffy for elevated ammonia levels in your tank.

Here’s why:

For a cat’s litter box to elevate ammonia levels in your tank, the litter box would  have to give off LOTS of ammonia.  So much so that you would likely be affected long before your tank. You’d probably have difficulty breathing and your eyes would be burning if you got anywhere close to the ammonia-laden room.

If ammonia levels were this high for an extended period of time, then I might be concerned about rising ammonia levels in your tank.  However, if the ammonia levels got anywhere close to a high level, you’d probably notice it and empty the cat’s litter box or at least move it outside.

Also, most cat litter products have an odor (i.e. ammonia) trapping component in them. Therefore any ammonia escaping would be minimal.

My advice: Keep the cat and don’t worry about the litter box being next to your tank. Or why not find the cat a new home…the litter box is taking up space where you could put another (or a bigger) tank!

Special thanks to Brandon R. from my Facebook page for his suggestion for this T.A.Tues.

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Comments for this article (7)

  • Stu Whisson says:

    Having both cats and marine fish has never been a problem. Cat’s do not nor would want to waste the time trying to get at marine fish. It’s a misnomer that cats will try and always catch the fish. They essentially have far better things and more fun things to catch than waste their time getting wet catching a fish.

  • Matthew and Jessica says:

    We have four fur babies (cats) and 40 gallon tank full of life. One of the cats, Purdy little, loves jumping up where the tank sets and watching the tanks activity. If she gets one close enough to the edge of the glass, she will swat at it. Some of the fish almost seems like they are teasing her to do it. However back to the advice we clean our litter boxes regularly and never have high ammonia levels in our tank.

  • John Rodgers says:

    I had a cat attempt to take a swim in an open top aquarium once.
    Metal halide pendent was swinging a little, and the cat little wet and scared, never attempted that again.

  • Pablo guzman says:

    I made a new refugium and i use silicone frim homedepot and i am loosing some corals. Do you thing the silico is the problem?

  • Pablo…could be. Some silicones say on the packaging that they are not meant for use in aquariums

  • Sean Miller says:


    Silicone products should be pure silicone and must not contain mold inhibitors to be considered aquarium safe. Usually GE Silicone I or II are recommended. I’ve used them in my tank without issue.

    That said, no silicone is safe until completely cured. Silicone II releases releases ammonia and methanol as it cures (both of which are very toxic to fish), and Silicone I releases acetic acid which is not quite as toxic, but still not great.

    You should check the packaging of the silicon you used. If it has mold inhibitors, you’re going to want to get it out of your tank. If it’s pure silicone, you should be fine, though if you didn’t let it dry long enough it’s possible that leaching chemicals have temporarily affected your corals.

  • Pablo guzman says:

    Thank you Mark and Sean Miller!!

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