Is Styrofoam Aquarium-Safe? (A Detailed Explanation)

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Insulation foam is a common solution for reef aquariums. If you’re unfamiliar with the idea, the premise is to spray or apply insulation foam to the back or sides of the tank, then push pieces of live rock, crushed coral, or whatever else you think looks interesting into the drying foam as a backdrop. Once the foam dries and hardens, it creates a live backdrop for your reef—and it also allows the unnatural looking plumbing, filters, and other equipment to be hidden from view.

Styrofoam is an inexpensive solution to beautify your reef aquarium, but is it safe? From a chemical standpoint, yes—foam is safe to put into your aquarium. If you are concerned about any chemicals or possible debris leaking into your tank, rinse the styrofoam off well before you add anything else to your tank, but you’ll also want to seal and waterproof the styrofoam before use anyway.

If there seems to be a problem, you can also add some extra carbon to your filtration system to cover your bases and help reduce the presence of any possible pollutants, but you’ll need to be wary of the effects this may also have on your aquarium’s ecosystem.

In general, though, it’s safe to use insulation spray foam as well as styrofoam in your aquarium as long as it’s not coated with anything. However, there are still some things to watch for.

How to Use Styrofoam in Your Aquarium

Any styrofoam that’s not coated is safe to use in your aquarium. Pink insulation foam is also safe to use. If you are concerned about using certain styrofoam options you’ve come across and worry about their quality and the safety of them being present in your tank, you can also use styrofoam from a cooler and simply cut it down into the pieces needed for your décor project. If a styrofoam product is labeled as “food safe,” it is also safe for aquarium use.

Silicone or glue can be used to keep the styrofoam stuck down to the glass to keep it from floating. When using these though, you’ll also need to ensure they don’t contain any particular chemicals that could be hazardous in an aquatic environment, such as mold or mildew inhibitors.

Is Styrofoam water-resistant?

Styrofoam and other kinds of rigid, expanded, and extruded polystyrene forms are water-resistant for short periods of time. However, they are not waterproof, so they will need to be waterproofed with sealants before exposing them to continuous moisture in your aquarium.

Some hobbyists have used epoxy, certain cement coverings, and silicone to seal and protect their styrofoam pieces, and they’ve even been able to incorporate substances like sand to add more texture and a nice appearance to the styrofoam before placing it to be a proper fixture in their setups.

Does Styrofoam Float?

Styrofoam is comprised of air pockets in between pieces of polystyrene (plastic) foam. This makes styrofoam much less dense than water—so, yes, styrofoam will float.

This is why it is so essential to make sure your styrofoam is properly weighted down and/or glued to whichever surface it’s being used on in your tank. If it were to become loose, it would rapidly pop up to the top of the water’s surface and likely cause significant damage to your aquarium environment.

How Do You Keep Styrofoam from Floating?

Any styrofoam décor you place in your aquarium is guaranteed to float to the top if you don’t do something about it. Essentially, you have two options:

Use the styrofoam underneath aquarium rocks, or place heavy bricks on top of it to hold it down. You can also hollow out “pockets” in your Styrofoam and fill them with gravel to reduce the overall buoyancy.
Glue the styrofoam to the sides of your tank (using a gel glue or silicone) if you are using it for a background.

Is Polystyrene Bad for Fish?

Polystyrene styrofoam is a relatively inert material that is generally considered safe for the fish that may be in your aquarium. When used as part of your aquarium décor, it doesn’t instantly leach any chemicals into the water, but the trick is to make sure that you use polystyrene that isn’t coated.

Many common hardware stores have a variety of polystyrene insulations available with an even wider variety of fire-retardant chemical coatings used on them. These coatings are full of chemicals and can leach into your water with the potential for harming your fish, so these types of styrofoam products are best avoided when it comes to aquarium use.

Polystyrene is sold as either extruded polystyrene or expanded polystyrene. The distinction is important because extruded contains refrigerant gas that leaks out of the foam over time, whereas expanded polystyrene contains no gas. However, there are still some concerns over expanded polystyrene containing styrene itself, which has been pegged as being carcinogenic in certain circumstances.

If you are using styrofoam in your aquarium, it is simply best to use plain, uncoated foam to avoid your new decor becoming a health hazard of any sort within your tank.

What Kind of Foam is Safe for Aquariums?

Rigid styrofoam insulation board is safe for use in aquariums as long as it is not coated with fire-retardants, anti-mildew, or anti-bacterial coatings. Styrofoam takes decades to decompose, and it typically doesn’t give off any chemicals at all, so it’s a very inert substance to place in your tank.

When choosing a type of styrofoam or other similar product for use in your aquarium, please keep in mind the preceding information regarding the risk factors and methods of ensuring optimal levels of safety for your aquatic environment.

Final Thoughts

Styrofoam and insulation foam are safe and convenient options for aquarium décor and backgrounds. Since styrofoam floats very well, you will need to weigh it down or glue it to your aquarium glass to ensure it’s secure for long-term use. When selecting styrofoam for your tank, be sure to use plain, untreated sheets to avoid any leeching of hazardous materials into your tank’s water.