Are Legos Safe For Aquariums?

There are 75 Billion Bricks Of Legos Sold annually in 140 Countries. Legos are very popular nowadays as well. So it raises the question of are legos safe for your aquarium. In this article, we will dive more into legos, plastics, and more you may want to know.

Yes, LEGO@ has announced that they are indeed safe for aquariums. The LEGO Bricks are comprised of hard durable plastics which make them safe for your fish tank.

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Knowing this it still would be a good idea to keep loose, floating LEGO@ bricks away from your fish in case they try to swallow them because after all if they can swallow them then they would.

Before considering placing your LEGOs in your fish tank I would consider sanitizing them as recommended by the manufacturer.

I’m sure you may also be cautious of the paint am I right? I bet the paint for LEGOs is still much better quality than fish stores. I would trust the paint quality.

How To Make Sure LEGOs Do Not Float In Your Fish Tank

When you place LEGOs in your aquarium you should consider gluing down LEGO pieces. Yes, the glue would be a very bad idea but we aren’t talking about the kind you used in school. We are talking about using epoxy as glue and also placing some sediment around the base of your LEGO structure as well.

Is Epoxy Resin Safe For Aquariums

Yes, Epoxy is safe for aquariums. In fact, it’s probably best for your LEGOs. Epoxy will not cloud up your aquarium which is a huge plus. Aquarium safe glue that I would use is the Super Glue.

Super Glue IS;

  • cheap
  • easy to use
  • longevity is fantastic
  • has a stronghold

Safe for fish?

Let’s talk about some things you could come into problems with if you do not know much about plastics, or LEGOs in your aquarium.

  • BPA
  • Algae Build Up
  • Small Openings
  • Aeration

BPA Chemical

Legos are made of sugarcane-based plastic rather than oil-based plastic. I’m sure you have heard of water bottles plastic left in the sun can cause plastic particles to pollute the drinking water with the BPA chemical causing it to not be safe. Think of your fish or tank mates with this aspect. It’s not a good idea to put plastics you do not know much about into your aquarium.

Best Plastics For Your Aquarium

The #1 PETE (polyethylene terephthalate) plastic is not what you wanna be using in your aquarium. The main reason is their longevity as they are one-use material. This means they are designed to use one time and throw them away or recycle. Water, soda, and juice bottles are typically made of #1 PETE.

  • #2
  • #4
  • #5

The #2 HDPE (high-density polyethylene) plastic is one that I would consider good for your aquarium. But, I would still double-check just to be safe. You will know if it is food-based plastic if it is marked FDA or NSF Approved. #2 plastics are milk jugs and also plastic buckets.

The #4 LDPE (low-density polyethylene) plastic is one that you can use in aquariums. But, just like #2, I would double-check to be sure since it is your fish we are talking about. Every company should have a section on their website or customer service that can answer your question. #4 plastics are shopping bags, store bags, juice box labels, and milk carton labels.

The #5 PP (polypropylene) plastic is also safe for aquariums. The #5 plastic is ideal for hot liquids since it has a high melting point. #5 plastics would be baby bottles, kitchenware, plastic cups, and microwave-safe containers.

Algae Build Up

Algae will build up with any decorations. Why would LEGO decorations be any different? The algae will not be that big of a problem if you were to add some algae eaters like the Corydoras Catfish.

Not all the bacteria associated with algae are bad. In fact, there are beneficial algae that are at work as well so if you want to clean the decoration I advise doing it one at a time so you do not kill the beneficial bacteria.

Small Openings

It’s important to leave some openings in your LEGO decorations for your algae eaters to clean them. Not having openings can mean not only good bacteria forming but also bad bacteria. Having decorations in your tank can decrease the overall water flow and the oxygenation as well as aeration.


Having less aeration can meaning opening more possibilities up for dead spots. Dead Spots are known to have fish poop, fish food remnants, and gravel build-up. Having less dead spots will increase the overall health of your tank.

Do Legos Float On Water?

The answer is yes and no. Legos do float on water when you put them in your aquarium. They will however eventually sink to the bottom so having them in there if you want them to float would be a bad call.

However, if you would like your legos to sink, like a sunken pirate ship, this is a good call. I would recommend that you consider adding some type of sediment on the bottom or inside of the lego decoration so the current will not move your legos around.

LEGO Fish Tank Decorations

For aquariums, it is advised to have coated, or pre-washed decorations.

Now it’s the fun part. I love seeing different decorations for other fish keepers. It’s interesting to see what others come up with for their own aquariums.

Some of my favorite ones that I enjoy seeing are ones with cities built on top. The plant escapes are good with much more foliage from the plants so I’m not sure if the sunken submarine would be one that I would personally go with.

This Mario Decorated tank is absolutely awesome. Personally, I enjoy the old-style retro games so this is a very cool setup for small fish like neon tetras. The castles are very well structured LEGO bricks but I do not think the rest are LEGOs. Most likely just placed to fit the design.

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