Are Glass Marbles Safe for Fish Tanks?

When tank owners are in the throes of starting their aquarium, or they fancy a change. The decorations inside are one of the areas they look at. While they may have live plants, plastic castles, and sand or small gravel as their substrate, they may fancy something very different.

Many tank owners think about using marbles, although, they are unsure about their use, and if it will harm their fish or their tank, and leads them to find out the answer to the question:

Are glass marbles safe for a fish tank? Marbles themselves are generally safe for use in aquariums. Their use can vary, and they do come with some quirks that are good and bad in equal measure. For the most, as a decoration point of view, marbles are safe to use in fish tanks.

Carry on reading, and you can see how to test which marbles are safe to use, how you can use them, and the plus sides and downsides of using them.

What Are Marbles?

Marbles are spherical balls of glass that have colored glass in their center. Children play with these kinds. Although, on most occasions, the kinds you purchase for aquariums are round on the top and flat on the bottoms. These are not marbles in the truest sense, yet they are made from the same materials.

Although there is a shape difference, when it comes to their consistency, there isn’t much difference apart from the color in the middle. No matter which shapes you use, they will be too large for fish to eat, so there are no worries in that department.

The one thing you will need to be careful of is that there are many marbles, which are not the glass and are a painted material. In some cases, this can be plastic and you do need to avoid their use. All marbles do need purchasing from a reliable marble supplier and not your local toy store.

Testing Glass Marbles for Aquarium Use

It doesn’t matter where you obtain your marbles. You will need to make sure they don’t affect the pH levels of your tank water. This is the same for anything you wish to place in your tank.

One quick way to test is to take a beaker full of water and test the pH level. Once you have this reading, place some marbles in the water, and let them stand overnight.

If there is no change, then they are safe to use in your aquarium. It is worth mentioning at this stage; there are many things not to place in your aquarium unless they are classed as safe for fish.

Here are some items you should not use in your fish tank straight away:

  • Plastics: You can smell plastic, and if anything smells like plastic, then it shouldn’t be added into your aquarium. Pet stores do sell toys made from this material, yet over time, these can leech toxic chemicals into the water. If you see plastic rated as food-grade, then this is okay to use.
  • Ceramics: Ceramics are the same as plastics in a way, and if they are safe for you to eat off, then they are deemed safe to add to an aquarium.
  • Wood: Although you can see wood, which has been added to tanks in stores and other places. These are treated and are safe to use. One wood that is okay to use is driftwood because it has spent time in water and will take time to decompose.
  • Sand from the beach: Sand can be used, but sand from the beach will be contaminated. When using sand, buy it from reputable dealers. To make your own, you need to soak and drain sand for a period of two weeks.
  • Shells and corals: If you have a freshwater aquarium. These can add calcium to your water and is a compound that isn’t required. Shells will change the pH levels of water and can cause issues with your fish.

Benefits of Using Marbles as Part of Your Aquarium Substrate

There are a few advantages of using marbles in your aquarium. One of the first being you can use them as anchors to hold accessories or fake plants into place. Some fish like to play with the plants and dig them up.

Bettas like to dig up or rearrange their tank, and this can be a huge issue with live plants.

The other benefits come from when you use them in breeding tanks as the main substrate. While adding a variety of colors is great, the spaces that the marbles create can serve a purpose in a tank as well.

Breeding tanks can make use of marbles in two different ways. Both of these can be beneficial to your breeding efforts, though differently, depending on if you are raising livebearers or egg-laying fish.

  • Safe spaces for egg-laying fish. Marbles provide a safe place for fish to lay their eggs until they hatch. The spaces between the marbles can offer areas that other fish can’t get into, which will allow the eggs to incubate in safety. This also means that the fry will have a safe place to hide from bigger fish for a while.
  • Safe space for fry. For live-bearing fish, the spaces in the marbles can offer a way for the fry to be safe in a tank of adults who see them as more snack food than young. While the main concern will be fish other than the parents, some fish species will eat their own young as readily as they will eat the young of other types of fish. Giving the babies a place to hide from other fish gives them a chance.

Another of the most significant benefits of using marbles in your aquarium is how easy they are to clean when your tank is empty. Because of their smooth surface, there is no scrubbing required, and some warm soapy water is sufficient. Bacteria can’t hide, and all you need is to rinse them properly before adding them back in your tanks.

Downsides of Using Marbles

One of the largest downsides to using Marbles is one of the major advantages when you use them in breeding tanks.

If you use round marbles rather than the half marbles, the problem is worse. If you are adding these as your only substrate, the gaps between them may be large enough for fish eggs or fry to hide, but they are also large enough for fecal matter and waste food to accumulate.

The issue here is that your bottom-feeding fish are unable to eat this food, and thus you will encounter algae growth. Even if you have algae loving snails, there is no way they can clear all the algae that cover the undersides of the gaps in the marbles.

If this accumulates too much, you will find that it is affecting your water condition. The only way you can resolve this issue is by using an aquarium gravel vacuum to clear all the waste out before it becomes toxic and kills your fish.


Marbles are safe to use in your aquarium, although it is advisable not to use them as your main substrate. Doing so can mean you face a continual battle to keep your tanks clean through vacuuming. Even then, this can only do so much, and you may face more frequent water changes as a result.

If you cycle your tanks regularly, then this is a better scenario, as they will be kept cleaner.

The best ways of using them are as decoration on top of other substrates such as sand to add some color to the bottom of your tanks.

Just be sure you purchase from the right place, they don’t change the pH of your tank water, and your fish will have something colorful to look at and play with.