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Should You Put LEGO in a Fishtank? (+ 5 Awesome Ideas)

A question people often ask is: should you put LEGO in a fishtank? There’s no one straightforward answer to this question, but we’re going to do our best to answer it.

Officially, The LEGO Group says that while its bricks are waterproof, LEGO pieces should not be used in a fishtank. However, lots of people do use LEGO to create bespoke fishtank displays. And as long as you exercise caution, you can too.

LEGO doesn’t provide a reason why you shouldn’t use bricks in a fishtank. On its official ‘Help’ page, it simply states it “doesn’t recommend” you do so. Here are some reasons why using LEGO bricks in your fishtank may not be a good idea:

  • Left in water for a long time, LEGO bricks can build up bacteria
  • Smaller pieces could come loose, blocking filters
  • Loose pieces could hurt fish

However, the type of plastic that LEGO bricks are made out of (ABS) is designed to be safe and non-toxic. After all, this is a building material designed to be a children’s toy, so it needs to be as safe as possible.

So, taking those pointers into account, LEGO can be used in a fishtank, but you’ll need to take good care of your bricks and your tank to do so.

How to safely use LEGO in a fishtank

Keep it clean

The worst thing you can do if you put LEGO in a fishtank is leave it to grow dangerous bacteria that could be harmful for your fish. LEGO pieces typically have hollow spaces; the ideal place for bacteria to thrive.

Ensure any LEGO structure you use as underwater decoration is removed regularly and thoroughly cleaned with a safe solution. Like any fish tank ornaments, we’d recommend LEGO is cleaned at least once a month, though more regularly is preferable.

Ensure bricks are secure

The last thing you want is a small piece of a LEGO model coming loose, so a fish could get it in their mouth or it ends up in a filter. It could cause endless problems that you really don’t want!

Don’t glue pieces together, but ensure they’re very secure. If small pieces, like flags and other typical flimsy bits, don’t feel very tight to the model, leave them off altogether. The safety of your fish is more important than how good a decoration looks. LEGO connections may perish over time when left in water for too long, so regularly check that the integrity of your model is still in tact.

LEGO Fish Tank Ideas

Despite The LEGO Group recommending against it, plenty of people do use LEGO bricks to decorate their fish tank. And, when it’s done right, it can look absolutely fantastic. We’ve scoured the internet and found some of the best LEGO fish tank ideas out there.

1. LEGO Minecraft fish tank

Image: NateQS/Reddit

Just how cool is this LEGO Minecraft fish tank shared by Reddit user NateQS? The main structure provides plenty of hiding places for the real-life fish in the tank, as well as looking visually striking. They’ve also created some puffer fish out of LEGO, added a fish tank and a minifigure.

We’d perhaps advise against having so many small pieces, such as the minifigure’s tool and the pufferfish details. But it’s great inspiration for anyone looking to create their own underwater LEGO Minecraft feature.

2. LEGO Harry Potter Quidditch fish tank

Image: kst8er/Reddit

If you’re a Harry Potter fan, what could be better than a Harry Potter-themed fish tank? This innovative Reddit user has built a custom Quidditch pitch, complete with goal posts, spectator stands and more. It looks fantastic! We’ve since had an official Quidditch set (79596), but this custom model looks way cooler. Hats off to the builder.

3. LEGO City construction site fish tank

Image: NigelGuy/Flickr

How about a LEGO fish tank that looks under construction? Flickr user NigelGuy has used LEGO City elements to great effect, creating a building site. There’s a digger and a crane, lifting pieces of a building into place. There’s even a minifigure crew, ensuring everything goes, er, swimmingly.

4. LEGO diver fish tank

Lego diver fish tank
Image: Totally-Tanked/Reddit

LEGO’s previously made a range of City sets all about underwater exploration. And so what sets could be better suited for putting in your LEGO fish tank? This one is from Reddit user Totally-Tanked, and it looks absolutely fantastic. The uniform colour scheme and placement of the objects is simply excellent, and the finished display looks stunning.

In fact, the LEGO City Ocean Exploration Base, used in the fish tank above, is still available to buy. You can get it directly from LEGO.com by clicking here.

A LEGO fishtank and LEGO fish?

If you’re still unsure about using LEGO bricks in a real fishtank, how about a fishtank AND fish all made out of LEGO? There’s the perfect set for you! LEGO Creator 3-in-1 31122 Fish Tank is exactly that. This budget-priced set (it’s only £25/$30) features a brick-built frame, housing five different tropical fish inside.

Much cheaper, and easier to maintain than the real thing, we’re sure you’ll agree.

The Best LEGO Sets to put in your fish tank

If you have a good selection of random bricks, the best thing you can do with your fish tank is to build something from scratch. That way, you know your tank is unique, with a model created from your own imagination!

But if you’d rather use something created by LEGO, some sets are better suited to put in a fish tank than others. These sets make better fish tank decorations than others:

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