Do Not Put Legos In A Fish Tank – Do This Instead

Do Not Put Legos In A Fish Tank – Do This Instead

The internet is full of aesthetic aquarium decor ideas that are brought to life using lego bricks. But despite its popularity among aquarists and the general people alike, lego decor is NOT the best option for your aquarium. Do Not Put Legos In A Fish Tank: The LEGO Group does not recommend using them in aquariums despite the fact that Lego bricks have no problem coming in contact with water. Decorations from Lego hoard dirt must be tightened to the bottom because of floating and have sharp edges, and can even trap fish inside. Fishes are exposed to swallow small parts. 

Legos are small, easily cleanable, waterproof, and can be used to create amazing ornaments inside the aquarium. However, there are a few concerns that need to be addressed before you start building your fish lego house. Legos can be unhealthy and dangerous for your fish, as well as for the fish tank’s environment in numerous ways. 

Let me address some concerns you might have surrounding the idea of using Legos as aquarium decor. Side by side, we will also let you in on some amazing alternative decor ideas for your fish tank.

Are legos safe for fish tanks?

Although The LEGO Group claims that their bricks will have no problem coming in contact with water, they recommend that we do not use them for decoration purposes inside an aquarium link. Hence, we can be certain that despite not being affected by water, legos can have a negative impact on life inside the fish tank. But how exactly can toys make kids damage life inside a fish tank? Well, let us consider a few angles.

Lego Castle – Fish Stash Or Fish Trap? 

The internet can provide you with a plethora of decoration ideas for your fish tank. Some of the most common aquarium decor ideas include different arrangements of lighting, underwater or aquatic plants, aquarium landscapes, waterfalls, and so on. 

However, one of the most popular decor options people are opting for these days is the underwater castle, and in order to help them build this type of ‘Atlantis’ inside their aquariums, people are turning towards the most accessible and easy-to-use building material known to mankind – Legos.

From Disney’s Cinderella castle to the one you can find in Super Mario, you have a wide range of options and themes to choose from if you are looking to build your fish a castle inside their underwater adobe. They are beautiful to look at, make the fish tank look lively, and can make the whole setup look more aesthetic.

The Downside To Lego Decorations

Firstly, you will need to tie down the lego decor with hooks, chains, or anything that can keep them fixed to the tank’s bottom and prevent them from floating around. As a result, you will find yourself tying them down with meshes of these chains or strings running throughout the entire area of the aquarium. 

This is something you cannot do especially if your aquarium is small in size. These strings can not only hinder the free movement of your fish but can also hurt them.

Secondly, even if you ditch the idea of using hooks or strings to tie them to the ground, you will still need to weigh them down in one way or another. Hence, you will have to place weights at certain points inside or on top of the decor. 

This might lead to the lego castle or decor collapsing or even breaking if you miscalculate the maximum amount of weight it can handle. 

Lastly, the lego castle inside the fish tank is always at constant risk of tumbling down, no matter how well it is made, placed, or tied down.

Your fish tank architecture structures made from Lego will get dirty in the meantime. Need to know how to clean your aquarium decorations from algae and build up dirt properly?  Check this post.

The movement of your fish inside the aquarium is constantly generating small waves inside the aquarium. Besides this, the fishes are bound to bump into the castle every now and then. All this external tension working on the castle can weaken its structure, which can lead to its fall. As a result, the castle might trap your fish inside its lego debris, and might even cause them to die either due to a direct impact or if they are trapped for a prolonged period of time.

Sharp Edges On Lego Bricks. 

In spite of being designed for children for ages 4 and above, lego blocks are found to have sharp edges instead of blunt or round ones. But why so?

Round-edged lego bricks make the joint-to-joint connecting points between bricks stand out. That means that the joints will look prominent and clearly visible to the observer. This takes away the appeal of the entire lego design which leads to a less aesthetic appeal of the whole decor. 

On the other hand, the joints between sharp edged bricks in a lego wall are very fine in a manner that they are hardly visible when you are observing them from a few feet away. This enhances the decor and helps give the entire piece a more aesthetic and realistic appeal to it.

Sharp edged joints are also known for their rigidity which helps build much stronger lego walls.

So we can conclude that those sharp edges on a lego block are there for good reason. And that is where our problems begin.

Inside a fish tank, the sharp edges can hurt your fish if they end up bumping into your aquarium lego decor. This could lead to cuts and bruises on their skin. Such accidents can lead to serious fatalities if they manage to damage important organs of your fish. For instance, an injury on or inside the gills of your fish can cause respiratory problems and even death.

There are also cases where you will find bits of broken lego pieces floating inside the tank. Even if your fishes are careful enough to not collide with the edges on the decor, there is a huge possibility that they might come in contact with the broken ones floating freely inside the tank. These floating lego fragments can get in their eyes or inside their mouth leading to all sorts of problems. 

The physical properties of lego bricks are not the only things that can endanger life inside the aquarium. People over the past few years have also gone on to debate about the chemical constituents that make up our beloved children’s toys. To be more specific, they have argued how these blocks and the chemical contents used in making them are toxic and harmful for children. 

What Are Lego Bricks And Decorations Made From? 

Ever since the early 1900s, legos have been made with something called Acrylonitrile Butadiene Styrene (ABS), which happens to be a thermoplastic consisting of a styrene monomer with the addition of an acrylonitrile monomer along with a butadiene monomer. 

The compound does not contain any known carcinogens and has no adverse health effects on exposure. Apart from legos, ABS is also used in the manufacturing of other toys, kitchenware, car parts, and also for 3D printing. Even the pipes you use inside your aquarium are often made from ABS-grade plastic. 

Legos use ABS as it is stronger and more resistant to color fading. Even inside an aquarium, the blocks can hold onto their colors and strength. Hence, there is no doubt that it is indeed the best option for making legos.

However, the polymer that makes up ABS (Acrylonitrile Butadiene Styrene) is a material that many people are not that fond of. The main reason for this is that it is a petroleum-based non-biodegradable plastic and hence, it is harmful to the environment. That being said, the real question is whether ABS is toxic or not. 

Are legos toxic? 

Like many plastic toys, legos too, once upon a time, contained traces of harmful chemicals. However, back in mid 2015, The LEGO Company announced that they will rethink their product making process and completely discard the use of such chemicals in their products. The company made a plan of investing a whopping $150 million for the development of new material for their product link.

As mentioned earlier, ABS plastic is the key material used in the making of legos. Although the individual components of this compound are toxic in nature, ABS as a whole is a stable resin that does not leach toxic chemicals. And Even though the material is not biodegradable, ABS is still recyclable. In fact, ABS is made from recycled ABS.

Although the material is not toxic, The LEGO Company plans on completely moving away from the use of ABS as raw material for its products by 2030.

What plastic is aquarium safe? 

High-density polyethylene (HDPE) is known to be one of the safest types of plastic for fish tanks. Compared to other plastics, HDPE is relatively stable and inert. It does not leach chemicals into the food or aquarium water no matter how long it is kept inside. 

Old plastic toys should not be placed inside the fish tank. They are toxic in nature and can harm the contents of the aquarium.

Apart from all this, it is to be remembered that no matter how safe the plastic is, it is still non-biodegradable, meaning that it will not mix up with the soil of the tank. Hence, the environmental damage being done by using plastic ornaments or decorations cannot be ignored. 

Alternatives to legos for aquarium decor

In case you are willing to change your mind about decorating the fish tank with legos, here are some alternative decor ideas for you to try out.

  • Turn your aquarium into the Bikini Bottom with the Penn-Plax Officially Licensed Nickelodeon SpongeBob Aquarium Ornaments. These ornaments include everything you need for a SpongeBob themed decoration, which includes SpongeBob’s Pineapple House, Patrick’s rock, Squidward’s house, and the Krusty Krab. These ornaments are made with safe and durable resins and can be easily wiped clean with some warm water. Link to AMZ.
Spongebob Fish Tank Decoration
SpongeBob Fish Tank Decoration Theme from
  • You can also go for a shipwreck theme by placing model ships or broken submarines at the bottom of the tank. Check out the models offered by Aquarium Equip and Slocme. They are as realistic as they will ever get. They are made from non-toxic materials. Link to AMZ.
Wrecked submarine underwater Fish Tank Decoration
Wrecked submarine underwater Fish Tank Decoration by
  • Decorate your fish tank with artificial plants. If your aquarium is small in size, and cannot accommodate all those large decors, it is in your best interest to opt for a greenish look for your tank. Not only is the decor easy to clean, but it is also made from non-toxic plastic and will not hinder the free movement of your fish. Link to AMZ.
Plastic Artificial Plants For Fish Tank
Plastic Artificial Plants For Fish Tank, plenty of options on Amazon
  • Ditch the usual plastic decor if you feel that it is unnecessary or just too much for your taste. Instead, place a layer of gravel at the bottom of the fish tank. Link to AMZ.
Fish Tank Decoration Gravel Options
Fish Tank Decoration Gravel Options From Amazon
  • Set up a waterfall inside the aquarium or on top of the tank. Waterfalls in aquariums are quite common. The design is simple yet has an unmatched elegance to it. They come in various sizes and designs. If you look hard enough, you will definitely find something for yourself too. Fish tank with Waterfall – amazon
Fish Tank Waterfall Decoration Setup
Fish Tank Waterfall Decoration Setup

Given how people are skeptical of using legos in aquariums, you too should think twice before using them as aquarium decor. Instead, you will be better off decorating your fish tank with the alternatives we have suggested. 

Recent Posts