Is Polymer Clay Safe for Aquariums (+ Better Alternative)

Using polymer clay to uniquely decorate a fish tank while saving money is a super appealing idea, but if you’re anything like me, then your excitement will quickly turn into wondering if it’s safe to use in aquariums.

Cured polymer clay may be safe for freshwater aquariums, but it has not been tested for long-term effects on fish. Some people use it in their tanks with no reported issues, and others caution against it because there’s a chance the center of the decoration won’t get fully polymerized.

I personally wouldn’t be comfortable putting it in with my own fish.

Are there safer clay alternatives for aquarium use?

Earthenware clays that are fired in kilns are considered safe for aquarium use. For example, many people use terra cotta pots as hides for their fish. Keep in mind that not all ceramic glazes are safe for aquariums, so you’ll need to do your research before adding any to your pieces.

If you don’t have a kiln at home, try checking with your local college art department or clay supply store to see if they offer a service for firing items.

Is polymer clay safe for freshwater aquariums?

Properly cured polymer clay is not immediately toxic to fish, but there have not been any tests done to see how it performs over time. It may be fine as there are reports of people using DIY decorations in their tanks and also in their ponds on fish keeping forums.

Keep in mind that the conditions (water parameters, how often water changes are performed, type of fish kept, gallons available, etc) are different across aquariums — what may work in one person’s fish tank may not work well in yours.

The safety of using it may be influenced by the length of time the polymer clay decoration has been submerged, the efficacy of the filter media used, and how many gallons of water the tank holds — more water would be more effective at diluting any unpolymerized oils that leach into the water.

Is polymer clay waterproof?

Polymer clay is able to remain submerged under water with no problems. It does not need to be sealed to be exposed to water. Some brands of polymer clay are more porous than others and will absorb tiny amounts of water.

If you use porous brand, then you may notice a white coating develop over time on the clay. This doesn’t happen to all brands, and it usually affects darker colors — it isn’t permanent, you can get rid of the coating by drying the clay out.

Is polymer clay safe for a planted tank?

While there is a lot of debate over the safety of polymer clay for fish, it seems to be more popularly experimented with in plant-only freshwater tanks based on the forums I checked out. That being said, I did notice that keepers overwhelmingly still recommend sticking to fired earthen clays for planted aquariums, also.

Is there any aquarium safe paint?

This is a tricky question to answer. While there are aquarium safe paints, they may not be suitable to use on polymer clay — I haven’t tested any personally to find out if they react with clay. Keep in mind that reactions don’t necessarily happen immediately, it can take months for the clay to begin reacting to paint.

Most of the paints that I could find that are listed as safe for aquarium use are spray paints, which are known to break down and dissolve polymer clay making it sticky to the touch. For example, many users on aquarium forums recommend Krylon Fusion as long as it’s fully cured.

If I was going to try putting a polymer clay sculpture inside a freshwater tank, then I would personally avoid using any paint.


  1. Spray paint will cause sticky polymer clay
  2. Handmade ceramics in fish tanks
  3. How porous is polymer clay

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