Aquarium gravel Vs. Substrate: What’s the difference?

Last Updated on January 18, 2021 by cmoarz

One of the things that most people often get confused with is the difference between aquarium gravel stones and substrates. These are two different things that serve different purposes. And even for plants, a substrate and gravel stones are necessary because that is how a plant stays anchored.

So what is gravel? The simplest way to explain it is they are rock particles. But they are also not like rough sand because the diameters of gravel stones used for aquariums are typically 3-25 mm. And anything smaller than 3 mm is not considered ideal for aquariums.

Gravel is what you would consider as fragments of rocks, and it comes in all types of different sizes. That is why it is essential to know what kind of gravel size you need for your aquarium. If you keep anything below 3 mm, there is insufficient water flow, and you get anaerobic areas in the aquarium. So always pick the right size for the best results.

It is also worth mentioning that gravel stones do not have any nutrient supplements like other stones. And other things require your attention. For example, some gravel stones can also affect the water’s Ph level, and some gravel stones need thorough rinsing before use. So different types of gravels have different specifications.

The best option for gravel stones is to use natural gravel without any coated paint. Most of the commercial gravel stones come coated with different colors using different materials. And although commercial gravel is safe to use, it tends to wear down the fish’s barbells. But you can avoid it if you use natural gravel stones.

Substrates, on the other hand, are also similar to gravel stones. But the primary difference between gravel and substrate is the latter has nutrient contents, unlike gravel. And these nutrients are essential for the fish to keep them healthy. The mineral content is beneficial if you have organic plants in the aquarium because it keeps them alive.

You can get substrates in different colors. And each color will have a different effect on the water. Most substrates tend to lower the Ph, general hardness, and the carbonate hardness of the water. So this makes it ideal for aquariums with live plants because they generally require a slightly acidic environment.

One of the best things about using substrates in your aquarium is that you don’t need any other material topping. And you can directly plant your choice of aquarium plant into the substrate, and they will grow.

Why use aquarium gravel and substrate

Aquarium gravel and substrate are integral parts of an aquarium, and there are many reasons you should consider using them. Aquarium gravel is vital because it helps the water filtration process. The aquarium water becomes dirty over time due to fish waste, plant debris, and leftover food. The gravel allows the growth of useful bacteria, eliminating all the impurities, and keeping the water clean. So it saves you from frequently changing the water.

Substrates are crucial for creating a sound environment for the fish. It allows them to make burrows, especially for the type of fish that likes to stay at the bottom. And in the process, they also get nourishment from the bacteria present on the substrates. It also helps shield the fish from the reflection of the glass.

Substrates are also very helpful for the fish when they lay their eggs. It provides a safe bottom surface for the eggs to mature and a home. And if you use larger substrates, it ensures that the eggs do not get eaten by the bigger fish because it stays intact between the gaps and out of reach.

As mentioned earlier, the substrates keep your aquarium plants rooted and alive. And it is crucial because the aquarium plants also keep the fish healthy and feed off the bacteria. And in general, substrates add to the aesthetics of the aquarium. You can add other decorations like plastic figures or plants, and it keeps them rooted and stable. The substrate and gravel bottom also hide all the other impurities like fish waste and leftover food.

Using aquarium gravel and the substrate is a great way to enhance the fish’s visibility as well. The stones come in different colors, and you can use them to bring out the contrast in the fish. And having a substrate and gravel stone makes your aquarium look rich and makes them look like a natural environment.

A few things to remember when using substrate

Although using substrates are suitable for your aquarium, it is worth mentioning that they are not always ideal. For example, if you want to use a grow-out tank to hatch eggs and grow the fry, having substrate in the tank will not help. The eggs are tiny, and it can easily get lost in the substrate.

For hatching eggs, you need a good clean tank with clean water, and it also requires constant water changing and cleaning. And if you have substrate, the eggs can get washed off as you clean the tank. So consider removing it if you plan on hatching eggs from the fish.

Another point to remember is that some people associate bright color substrates with stress problems on the fish. And when the fish is stressed, it also weakens the immune system, and it becomes prone to diseases or can die easily. Bright colors like pink, red, orange, etc., are not natural color stones you would find in a natural environment where fish thrive. And that is the reason why it can cause problems for different types of fishes.

So these are things to consider before deciding to use gravel or substrate. Both have many similarities, but the primary difference is the nutrient content in the substrate, which is absent in gravel stones. And based on the type of fish you have, you can either choose to use one or both by layering them up with your choice of color.


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!