Can You Put Legos in A Fish Tank? What Makes it Safe?

Hi, this is your friend Clifton Ervin, the founder and chief editor of this site, Aquariumwolf. I completed my graduation in marine biology and became...Read more

The first thing to consider when decorating a fish tank is safety. So, carrying out necessary research can help prevent possible errors. When picking aquarium ornaments, the first idea is to use Lego bricks.

These materials are an excellent way to beautify such tanks, but can you put Legos in a fish tank? Are they safe for the fish? For several reasons, Legos are safe to be used as an ornament in an aquarium. One of the notable ones is that the majority of Lego bricks are made of ABS material, which is considered safe for the creatures in the aquarium.

There are more facts about the use of Legos for aquariums in this article. Moreover, we’ve also discussed the proper size of the Lego aquarium and more. So, keep reading to learn more.

Different Sizes of Aquariums

Fish tanks come in a variety of ranges or capacities. It’s possible to get a fish tank of just 1 gallon, or up to 100 gallons.

The aquarium ornaments are not the only things to consider regarding the safety of your fish. The capacity of the fish tank also plays a vital role. The truth is, your fish feels more comfortable in a spacious aquarium than in a smaller one.

In a smaller environment, fishes get aggressive due to stress, which could result in specific health issues. Moreover, the more spacious the aquarium is, the more Lego bricks you can install.

Here are the popular sizes of fish tanks that are available for purchase:

  • 1-to-4-gallon aquarium
  • 5-to-10-gallon aquarium
  • 11-to-20-gallon aquarium
  • 21-to-40-gallon aquarium
  • 40 + gallon aquarium

But not all aquariums support much decoration, particularly with Lego bricks. For example, the 1-to-4-gallon aquarium lacks enough space to contain too many ornaments. The 5-to-10-gallon aquarium may seem okay for decoration, but the suitable size begins with the 11-to-20-gallon aquarium.

Here’s a table to simplify the information:

Capacity Width Length Height
3 Gallon Aquarium 6 Inches 12 Inches 8 Inches
5 Gallon Aquarium 8 Inches 16 Inches 10 Inches
10 Gallon Aquarium 10 Inches 20 Inches 12 Inches
15 Gallon Aquarium 12 Inches 24 Inches 14 Inches
20 Gallon Aquarium 12 Inches 30 Inches 16 Inches
25 Gallon Aquarium 12 Inches 34 Inches 16 Inches
30 Gallon Aquarium 13 Inches 36 Inches 16 Inches
40 Gallon Aquarium 13 Inches 48 Inches 16 Inches

With the above table, you can easily picture what each aquarium looks like and how many Lego ornaments it’ll require. One thing you should note, however, is that the measurement cited above doesn’t include the tank hood’s height. Also, this data is particular to rectangular-shaped fish tanks.

Putting Legos in A Fish Tank

While most aquarium owners believe installing Legos in their fish tanks is okay, the LEGO Group says otherwise. With this in mind, can you put Legos in a fish tank? Will they affect the well-being of the fish in the aquarium?

Putting Legos in A Fish Tank

If you apply caution, you can use these ornaments to decorate your fish tank.

The LEGO Group doesn’t support using Lego bricks for aquarium decoration. But it also didn’t state why the bricks shouldn’t be used. On the Help page of the company’s site, you’ll find the phrase “doesn’t recommend” the motion.

Here are a few reasons the company doesn’t support using these bricks

  • Blocked filters – Smaller pieces of the bricks might be displaced to the filter areas and could cover them.
  • Bacteria build-up – The company believes that keeping these bricks in water for a long time could result in the build-up of bacteria.
  • Fish getting hurt – Chances are that loose pieces of bricks could negatively affect fish.

Meanwhile, these bricks are made of ABS plastic, which is non-toxic and safe. The safety of this material is not questionable, given they were created as kids’ toys. But, there’s a need to exercise caution to ensure the safety of the fish. Let’s address some relevant things you should look for in this case.

Best Legos in A Fish Tank

Before we talk about the best Lego ideas you can opt for, let’s consider the shape of the bricks. To protect the fish in the aquarium, install bricks with curved edges.

Using Lego bricks with sharp edges could be a potential danger to the fish.

Several Lego ideas are available on the market, but here are your best picks.

Lego Diver Aquarium

The Lego team had previously created some great options for underwater exploration. This set of ornaments is known as the City set. It comes with a similar theme as the bed of the sea, making it one of the best options available.

Lego Harry Potter Quidditch Aquarium

The Harry Potter Quidditch aquarium is mainly designed to simulate the Harry Potter environment. It’s another great option from Lego, which is mainly appreciated by Harry Potter fans. This is an upgrade to the previous official quidditch of the company, with a more appealing appearance.

Lego Minecraft Aquarium

Here’s another stunning Lego fish tank idea from NateQS, a Reddit user. The design creates many spots where the creatures in the aquarium can find refuge. This option includes some Lego puffer fish and a Minifigure added to the aquarium.

Lego City Construction Site Aquarium

As the name suggests, the idea here for a city construction site is to create a scene similar to a construction site. Here, you’ll find a crane, digger, etc., mimicking the construction of a building. Also, to make it look more realistic, there’s a crew of Minifigures.

Sanitizing your Legos

Cleaning and sanitizing Lego bricks is not such an easy task to carry out. You may use soap or detergent for the cleaning process. To sanitize them, simply add white vinegar.

There are different cleaning and sanitizing approaches to Lego bricks. Some folks prefer to use machines, and others fancy the handwash method. Others use special procedures to carry out this task.

To begin, here’s what you can do:

Separate All Pieces

This step might be a bit tasking, but this is what is required for ideal cleaning. You can start by putting aside the stickered pieces, leaving the others on one side. Use a soft cloth or brush to remove the dirt from the stickered pieces. This is quite necessary to avoid the stickers coming off or loosening by water.

Wash with soap or detergent

For the rest pieces, simply place them in a sink, basin, or bathtub, depending on the quantity. Fill up the container with warm water. With soap or detergent, wash them by moving your hands around in the water. Washing them singly isn’t necessary, except on your terms.

Use White Vinegar

The role of white vinegar here is to sanitize the bricks. White vinegar is one of the easy ways to disinfect the material. To use the sanitizing agent, place the Lego bricks in a container filled with hot water.

Pour about ¼ of white vinegar into the container and leave it in that state for the next 10 minutes. Once the period is over, simply rinse off the vinegar.

To dry the bricks faster, you can place them on a thick towel in front of a standing fan and let them air dry.

Another method you can use is displayed in this YouTube video.

Things To Avoid In A Fish Tank

Perhaps you want to change the looks of your fish tank but are still skeptical about what to use. If this is the case, then you’re not alone.

Things to avoid in a fish tank

Here are some ideas on materials that could be dangerous to the fish in the aquarium:

Consumable Materials

The only consumable object allowed in the fish tank is the food you give your fish. Aside from this, any other consumable substance is a potential threat to the health of the fish.

Some of the consumable substances could release toxins after some time. So, be sure of the possible side effects of the materials you place in the tank.


Ceramics with the sign “dinnerware safe” are okay to use in an aquarium. This means that if the ceramic material is edible, placing it in the fish tank will be a bad idea.

Always be sure the object is not harmful to the inhabitants of the fish tank. However, ceramic rings are a different thing; they work as a bio-media and maintain the nitrogen cycle in your aquarium.

Beach Sand

You can use treated sand in your aquarium, as it is a good substrate. However, the idea of using beach sand can eventually harm the fish in the tank. This is because of the presence of chemical residue in the sand,


Using wood in your fish tank is not out of place, provided the wood is treated. Untreated wood should not be used in an aquarium. One of the notable things this does is to alter the water chemistry. When this happens, the water’s inhabitants are exposed to danger.

Though driftwood works fine as an aquarium ornament, it should be the hardwood option. This is necessary as it’ll take a long time for such wood to decompose in the water.


Improving the look of your aquarium doesn’t end with selecting the best ornaments, such as Lego bricks. You also need to consider the safety of the fish in the aquarium.

In this case, some fish tank owners recommend Lego bricks, but can you put Legos in a fish tank? Putting Legos in a fish tank is safe if you follow the correct procedure. It’s also advisable to clean and sanitize the bricks before use.

Hi, this is your friend Clifton Ervin, the founder and chief editor of this site, Aquariumwolf. I completed my graduation in marine biology and became an Ichthyologist. One of my favorite hobbies is aquarium keeping; therefore, I love to talk about fish keeping, breeding, food behavior, etc., and much more relevant to aquarium maintenance. I have created this site Aquariumwolf, to share my 20 years+ of experience and knowledge with all new to this journey.

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