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Is PLA Safe To Use in Salt Water Aquarium?

You’ll learn what PLA is and how to use it safely in your aquarium. We also cover what happens with PLA when it interacts with saltwater and give you pointers on making your PLA waterproof.

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What’s a person to do when they want to update the look of their aquarium but don’t want to spend a ton of money on aquarium decor? For many, 3D printing using polylactic acid (PLA) is a common thought amongst aquarium owners, but is it safe to use?

PLA is safe to use in saltwater, but it’ll degrade quickly if you aren’t careful. Waterproofing techniques, such as wax or a fixative spray can help deter saltwater from eating away at the PLA. Additionally, PLA shouldn’t include any additives that can be harmful to your aquarium life.

In this article, you’ll learn what PLA is and how to use it safely in your aquarium. I’ll also cover what happens with PLA when it interacts with saltwater and give you pointers on making your PLA waterproof.

Using PLA Safely in Your Aquarium

Polylactic Acid, or PLA for short, is one of the most common materials used in 3D printing. It’s also the least expensive and most environmentally friendly. PLA material is derived from crops like sugarcane and corn, so not only is it biodegradable, but it has a sweet smell to it too.

It isn’t hard to safely create a 3D creation for your aquarium with PLA. However, some things can go wrong if you aren’t careful. 

For starters, if you aren’t printing the design yourself, you’ll need to watch out for harmful additives to keep your aquarium life safe. These additives are what make things glow in the dark, for example. And while a glow-in-the-dark decoration may look cool, it could actually hurt your fish.

PLA also tends to ooze when it first comes out of the printer, so if you’re printing it yourself, you must let it cool down completely before placing it inside the aquarium. However, if you purchased the PLA decoration, you likely wouldn’t run into this issue.

What Happens When PLA Interacts With Saltwater?

Because it’s biodegradable, it breaks down naturally when submerged in water. When PLA interacts with saltwater, it breaks down quickly due to the mineral content in the water. To avoid this, aquarium owners will waterproof any PLA they want to use in their tank.

Freshwater is generally preferred when it comes to PLA aquarium decorations. This preference stems from the fact that freshwater doesn’t contain the salty minerals that saltwater does. Those salty minerals facilitate the breakdown of the biodegradable composition PLA is made of. This doesn’t mean the saltwater makes PLA unsafe; it just means it won’t last as long as it would in freshwater. 

When in the right conditions, your PLA can last years in an aquarium. However, other factors can shorten the piece’s shelf life.

PLA’s biodegradability makes decomposition a common issue. The components of the PLA absorb water much quicker than other materials, making it susceptible to pieces breaking apart and mold/mildew to grow.

Freshwater tanks are ideal for PLA aquarium decor because they don’t contain salt or other minerals to facilitate the decomposition process. As the PLA continues to absorb water, its integrity weakens, and the print develops a rough texture. It can also form bubbles and become stringy too. The print will also become more brittle, and it can swell up over time.

How To Make PLA Waterproof

There are several ways to waterproof your PLA to make it last longer. Waterproofing your PLA will also deter the decomposition process from contaminating your tank. 

More so, waterproofing your PLA will protect it from UV rays and make it more difficult to sustain any other damage.

To waterproof your PLA print, consider using wax or a fixative spray.

Coat With Wax

3d-printed pla items

Wax is perhaps the most commonplace option for waterproofing your PLA print. Not only is it used to waterproof aquarium decor, but wax is a standard waterproofing method in a variety of other industries too.

Additionally, wax forms a barrier between the object and the water, but it waterproofs by smoothing out rough edges.

You should coat any part that’ll interact with the water with wax. If you aren’t sure if a part will be constantly exposed to the water, cover it anyways.

The idea is to protect the main surface as it’s the part that comes into contact with water the most. On the other hand, if an object is just floating in the water, you’d only need to place a wax coat on the bottom part of the piece.

To coat your creation with wax, follow these steps:

  1. Clean your piece and melt your wax. Make sure your 3D creation is completely clean, so you get an even coat of wax. Melting your wax will also help you get a more even coat.
  2. Let the PLA creation dry completely. You need to give the PLA time to dry adequately. This way, you won’t burn your hand during handling, and it’ll be easier to remove excess wax.
  3. Remove extra wax. While this won’t affect the integrity of your PLA piece, it’ll weigh it down. It may look unsightly too.
  4. Check for leaks. Before finishing the process, you need to check for leaks. To do this, all you need to do is fill a container with water and dip the PLA in. Leave the PLA in the water for one minute and then remove it. If you see water permeating, you’ll need to add a second coat.
  5. Let it dry and give it a good clean. Once you’re satisfied with the waterproofing, you’ll need to let it dry completely and then clean it one more time. After all of that, you’re ready to place it into your aquarium.

Keep in mind that the wax will be hot, so you should use gloves while completing this process. You also need to be sure to hold on tightly to the object as the wax will make it very slippery.

Use a Fixative Spray

If you don’t want to fuss with wax, a fixative spray is a convenient alternative. All you need to do is spray the surface of your PLA and let it thoroughly dry. Fixative sprays also come in a glossy, satin, or matte finish, so you can choose whichever matches your overall vision.

Several brands of fixative sprays will do the trick, but this Mod Podge Clear Acrylic Sealer (available on comes highly rated by consumers. It’s available in three different finishes and is also easy to use. Customers recommend this specific sealer because it dries quickly and it doesn’t leave sticky residue anywhere.

Parting Thoughts

PLA is a safe and widespread material used in aquarium add-ons. Unlike other 3D printing materials, it’s biodegradable and entirely harmless for fish and different aquarium life. 

However, you need to take extra care when using it in a saltwater tank. As long as you’re mindful of any added ingredients and you properly waterproof your PLA creation, your aquarium can house your creations for years to come.

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About Ben

I started 3D printing since 2013 and have learned a lot since then. Because of this I want to share my knowledge of what I have learned in the past years with the community. Currently I own 2 Bambulab X1 Carbon, Prusa SL1S and a Prusa MK3S+. Hope you learn something from my blog after my years of experience in 3D printing.