Sand vs Gravel. What is the best aquarium substrate?

When choosing the substrate for your aquarium you dont want to make the wrong decision since a change later on is quite hard to manage. That’s why we will tell you how to find the ideal substrate matching to your requirements. Why we think in most of the cases sand a better choice than gravel you can read below.


The substrate is an important part of our aquarium ecosystem. It is providing hold for the plants, filters the water and buffers nutrients & bacteria. In trade, a distinction between sand and gravel substrate is made. We will talk about the differences between these two varieties below.


When choosing a substrate it is important that the material is not hardening the water. Therefore lime-free sand or gravel must be used. This does not only apply to the substrate but also to stones used as decoration. Nothing is more annoying than setting up the aquarium and than realizing in retrospect that something is hardening the water.

If you want to be sure that the material is lime-free you should buy commercially available aquarium sand or gravel. Then you can be sure that no hardening takes place.

However if you prefer to use the cheaper substrate from the hardware store, we recommend that you test the gravel or sand for its calcareous content as described below. With sand from the hardware store you have to be sure that no additives such as fungicides are included.

Testing for lime

If you sprinkle concentrated acetic acid or hydrochloric acid on calcareous material it starts to bubble. Unfortunately simple household vinegar is not strong enough to carry out the test. You may get concentrated acetic acid or hydrochloric acid from your local hardware store where it is often found in the cleaning products section.

Grain size

Substrate is distincted depending on the grain size into sand or gravel. There is no fixed separation between the two but generally speaking gravel has a grain size bigger than 1.5mm. Everything smaller is considered as sand.

But when should you use sand and when do you use gravel as substrate for your aquarium? And why is sand the better option in case you are unsure?

Sand (0.4-1.5mm)

  • Advantage – fish restrictions

    For many bottom dwellers sand is the best option. Since sand has no sharp edges, there is no risk of injury to our tank inhabitants. Fishes whose natural behavior requires digging in the ground depend on sand, as otherwise they can injure themselves when trying to dig in gravel. Especially armored catfish thank the owner if they can root in the ground and will stay healthier.

  • Advantage – no food leftover

    Another advantage of sand substrate is the dense packing. As a result, food residues can not disappear into the spaces between grains and thus contaminate the water.

  • Advantage – plants holding

    Some plants prefer sand as soil over gravel. This is especially true for aquarium plants whose roots are not strong enough to wind throught the heavy gravel.

Gravel (>1.5mm)

  • Advantage – leftover food

    What was called an advantage on the sand side can also be an advantage on the gravel side. With gravel, food leftovers easily settle in the spaces between the grains. These food leftovers serve as breeding ground for bacteria which are necessary for the biological equilibrium.

  • Advantage – easy cleaning

    Gravel is easier to clean with suction because it is not so easily sucked in as sand. There are several tools that work fine for gravel but cannot be applied to sand.

So why is sand the better aquarium substrate? The main benefit is that you have all options open when it comes to fishes. If you for example want to get corydoras later on you will regret the decision to use gravel instead of sand. The other pros and cons actually equalize.

Last but not least: How much soil is needed?

From experience we know that a substrate height of around 6cm is a good choice. With this height most of the plants get enough hold. However if you want bigger plants in your tank you might want to use a higher substrate height.

With our volume and substrate calculator you can easily enter the aquarium dimensions and find out how much substrate is needed for your tank.


We hopefully could get you some points on when you want to use sand or gravel. In the end if you are still unsure, let’s decide your taste.

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