Cat Litter for Aquarium Substrate or Is It Toxic?

Last Updated on July 15, 2022 by cmoarz

Someone asked me if cat litter would be a good option for their aquarium substrate and if it was safe. I thought that was a really interesting question. Why would someone want to use cat litter for aquarium substrate? Well, for one thing, it’s cheap! You can get 25lbs of the stuff for only a couple of bucks, But the real question is, should you?


Can you use cat litter as an aquarium gravel substrate?

As it turns out, You absolutely can use cat litter as an aquarium gravel substrate for planted tanks and even tanks with fish in them!

Many cat litters are made of the same material as many aquarium substrates, specifically things like laterite and clay granule. This makes cat litter a perfect, cheap alternative to more expensive aquarium substrates, and it won’t be turned to mush either.

But there are a few caveats you will need to know about before you make your decision as not all cat litters are made equal.

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What to avoid when you are using kitty litter substrate

  • Avoid any cat litters with any sort of clumping agent in them as these can be toxic to fish and plants.
  • You’ll also want to avoid any cat litters that have been treated with fragrances or perfumes as these can also be harmful to your aquatic friends. So scented varieties are completely out.

The best type of cat litter to use for your aquarium substrate is an unscented, non-clumping variety made from 100% natural materials and zero additives.

Anything else risks harming your fish or plants so it’s best to just avoid them altogether.

  • You should avoid just dumping it into your tank. This type of substrate needs to be soaked several times to remove the powdery substances that will cloudy up your water and potentially harm your fish if left in.

Much like sand, You will want to keep rinsing kitty litter until the water runs mostly clear. You may never be able to get rid of all of the cloud, but the bulk of it should be removed before adding it to your tank.

Water clarifiers aren’t really an option here because they will just get stirred back up again as your plant and fish around.

  • This type of substrate should be avoided for bottom feeders. Fish like corydoras and plecos tend to spend a good deal of their time rooting around in the substrate and slithering around on their bellies which could end up cutting thems on these sharp substrates, as cat litter isn’t polished smooth like many substrates.

This can lead to infection and potentially death so it’s just not worth the risk. The same goes for any other type of fish that tends to burrow or spend a lot of time on the bottom of the tank.

While it may be tempting to use because it’s so cheap, I would recommend avoiding kitty litter substrate for these types of fish.

  • Be aware of the pH, GH balance, and hardness levels. Cat litters can vary greatly in their pH and hardness levels so it’s important to do your research before adding them to your tank. If necessary, Test them in an empty tank or small container and test the water periodically to make sure the levels are where you want them to be before adding your fish.
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Is kitty litter as a substrate good, and should you use it?

Assuming you purchase a mostly pH-neutral and safe variety of cat litter, kitty litter can make a great substrate for your aquarium!

Your plants will be able to root well in it and, as long as you avoid using any clumping cat litter or scented clay litter, your fish will be safe and happy too!

Keep in mind that these types of clay cat litter substrates aren’t considered bioactive. You will need to add fertilizer for your plants in the form of root tabs or liquid.

On the other hand, The litter itself provides tons of porous material for beneficial bacteria to colonize and do their filtration job.

It may also be worth adding a layer of something else on top of the litter, such as a heavier Flourite stone which helps make planting easier and keeps the dust down, And even a bottom layer of peat for extra bioactive elements.

But if you’re looking for a cheap, effective substrate for your aquarium then kitty litter is definitely worth considering!

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Why would someone prefer cat litter over a normal aquarium substrate?

The biggest reason people might choose to use cat litter over a traditional aquarium substrate is that it’s much cheaper.

Aquarium substrates can be quite expensive, especially if you’re trying to get a deep substrate layer in a very large tank. Cat litter is a fraction of the price.

Another reason is that some types of cat litter can provide a more natural look for your aquarium than gravel or sand. This can be especially true if you choose an earthy-toned variety of kitty litter.

And finally, cat litter is often praised for being much easier to plant in than gravel. The larger pieces of cat litter make it easier for plant roots to grab onto and the loose nature of the substrate allows for easy root growth.

It’s also much harder for fish to uproot newly planted plants in cat litter than it is in gravel.

So there are definitely some advantages to using cat litter as your aquarium substrate! Just be sure to do your research first and choose a safe, neutral variety of kitty litter to use, such as none climbing unscented special kitty brand.

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Will aquatic plants and planted tanks do well with cat litter as substrate?

Yes! Aquatic plants will do very well in cat litter substrates, especially if it’s deep, layered, and well fertilized.

The loose, porous nature of the substrate allows for easy root growth and the larger pieces of kitty litter make it easier for plant roots to grab onto. Just be sure to choose a safe, neutral variety of kitty litter to use.

And don’t forget to add fertilizer for your plants in the form of root tabs or liquid. Since cat litter is not a bioactive substrate, you will need to add fertilizer to your plants in order for them to thrive.

But if you’re looking for a cheap, effective way to create a planted aquarium then using cat litter as your substrate is definitely worth considering!


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!