Choosing a Freshwater Aquarium Substrate

The material you use to line the bottom of your fish tank is called substrate. The substrate you choose can have a significant impact on the aesthetic look of your tank as well as the health of your fish and live plants. There are four important aspects of the substrate that you should take into account when selecting which is right for you: particle size, color, reactivity with the water, and its effect on your fish. In this article you will learn the benefits and drawbacks of the most common types of substrate in regard to these aspects so you can choose the one that is right for your tank.

Particle Size

Substrates vary widely in terms of particle size – everything from sands consisting of very tiny particles to larger river rocks. Large particle substrates allow more uneaten food and waste to penetrate into it leading to toxic build ups if not cleaned. Small particle substrates can compact which may lead to areas that lack oxygen. These areas can eventually release hydrogen sulfide – a substance that is extremely toxic to fish.

The size of the particles also has a big impact on the health of the fish and the ease of cleaning. For instance, some fish like to scoop the substrate in their mouth and move it around. It is not a good idea to mix these species with sand because the small particles can irritate them. Sand can also be somewhat difficult to clean as the small particles often get vacuumed out of the tank along with the waste. On the other hand, some fish enjoy making nests or homes out of the substrate and in these instances, large particle sizes would not be conducive to this habit. As you can see, it is important to research the specific needs of your fish when considering the appropriate particle size.

Color

When it comes to choosing a color of substrate, you have many options to choose from ranging from neon-colored substrate to natural colors. The color of the substrate is a very personal choice, so choose what you like best. Many people love seeing bright pink gravel while others would cringe at the thought of such an unnatural looking substrate. One common use of a substrate’s color is to enhance the color of the fish. Darker colors tend to make a light-colored fish look brilliant. On the other hand, a light-colored substrate can wash these same fish out, but can also make dark-colored fish stand out.

Overly dark substrate can reduce how large the tank looks in a similar fashion to painting a room in your house a dark color. For this reason, some people use lighter colored substrate to make the aquarium feel more open and bright. You may also want to consider how the substrate will look once it becomes dirty. Brownish-colored substrate tends to hide fish waste more than white substrate, for instance.

Reactivity with Water

Some species of fish require certain water parameters. For instance, many African cichlids prefer a higher pH. One way to raise the pH in your aquarium is to use a substrate that buffers the water (for example, crushed coral). This is why you see so many African cichlid tanks that use crushed coral as their substrate. Peat moss, on the other hand, has the exact opposite effect – it lowers the pH. This is good for fish species such as angelfish that require a lower pH level in the tank.

Impact on Fish

It is important to consider how the substrate you choose will impact your fish. Not only can it react with the water as discussed above, but it can also harm your fish if, for instance, you choose glass chips with sharp edges as your substrate. Also, very light-colored substrate can sometimes spook your fish, especially when it is combined with bright lighting. This may cause them to hide and dull their color. Overall, you should read about the natural habitat and behavior of your fish. Then you can find a good balance between what is pleasing to your eye and what it pleasing to your fish.

Specific Substrate Choices

Now that we have discussed how to pick your substrate in general, we will look at some of the more common substrates:

No Substrate

While this may not be the most beautiful choice, it does serve a purpose. Many breeding tanks, hospital tanks, and tanks used to raise fry use a bare bottom. It makes it easy to catch fish, it is easy to tear down, and it is very easy to clean. However, an obvious con is that there is nothing to hide the waste and uneaten food. It can also be stressful to fish that are used to digging. In some cases, fish become spooked by their own reflection so it is wise not to use a bare-bottomed tank unless you have a specific reason for doing so.

Gravel

Gravel is by far the most common substrate used in the hobby and it is the most conducive to cultivating a “natural” appearance in your tank. Gravel comes in a multitude of colors and is often favored by young children for this very reason. It also comes in various particles sizes. Larger gravel sizes can allow a great deal of waste to penetrate it making it difficult to keep the aquarium clean. This is one reason why many aquarists prefer smaller-grained gravel. It is also important to not purchase gravel with sharp edges, especially if you have fish that dig or sift the substrate. Substrate may also not be the best choice if you have catfish in your tank – because they do not have scales, their skin can be damaged by rough substrate.

Sand

Sand is a very beautiful substrate. There are many types of sand that can be used – everything from play sand to black Tahitian Moon sand. The lightly colored sand really sparkles in an aquarium and sand in general gives a very smooth look to your aquarium. Fish with delicate barbells (such as corydoras catfish) also prefer sand over gravel.

Sand also has several aspects that can make it a difficult substrate to work with. The most glaring problem is that it usually has very fine particle sizes. It is often so fine that you will end up siphoning a good deal of it up with your water when you vacuum your tank. This problem can be solved in one of two ways. First, you can simply replace the sand over time. Second, the debris will tend to sit on top of the sand due to its small particle size. You can, therefore, siphon the waste off the top of the sand by holding your siphon a couple of inches above the surface of the sand (although you should disturb the sand slightly so it does not become anaerobic and black).

You need to be careful with your filter choice if you choose sand. If you disturb the bottom too much and fling sand all over your tank, particles of sand can become trapped in the filter. Be cautious when cleaning or rearranging your tank for this reason. Also, under gravel filters generally cannot be used with sand. The other problem (and ironically, the property of sand that makes it so beautiful) is that it is typically light-colored. Dirt and waste really show up in light-colored sand. Anyone who has ever seen a sand-bottomed tank that has not been vacuumed in a while can attest to this.

Sand is also susceptible to compacting. This makes it a poor choice for a planted aquarium as the roots can have a difficult time penetrating this compacted substrate. If you do decide to mix plants and sand (again, not recommended), then at least carefully mix up the sand every once in a while to prevent compacting.

Crushed Coral

As discussed above, crushed coral raises the pH in the aquarium. Therefore, it is not a good choice for fish that prefer water with a low to neutral pH. It is perfect, however, for fish such as African cichlids. It also gives a salt water “feel” to a fresh water aquarium. If you need the buffering that crushed coral provides, but your fish prefer sand, you can use coral sand as your substrate. One major problem with crushed coral relates to its light coloration which again does not hide dirt and debris. This can be remedied by frequent vacuuming.

What if you Have Plants?

This is a topic unto itself because the type of substrate you choose for a planted tank is affected by many factors. You have to consider whether the substrate can be penetrated by plant roots and whether it will provide enough support for the plants themselves. Substrate in a planted tank also needs to provide nutrients for live plants so they can grow and thrive. Refer to the article list on www.ratemyfishtank.com and read the article regarding choosing a substrate for your planted aquarium.

For a general idea of planted tank substrate options, refer to this list:

EcoComplete – contains all the mineral nutrients plants require to thrive and grow; natural-looking and long-lasting

Fluorite – clay-based substrate with high iron content; not recommended for plants with delicate roots

Laterite – clay-based substrate that can absorb and store nutrients; may cloud tank water

Aquasoil – made of round grains to allow for circulation; acts as a passive filter; many options available

Sand – looks natural, inexpensive; can be combined with other substrates in layers

Potting Soil – inexpensive and natural; may compact and lead to circulation problems

Conclusion

The beauty of cultivating a freshwater tank is that you have so many options for customization. Not only do you get to choose the size and shape of your tank, but you also get to pick what goes inside it – this includes everything from your fish and decorations to the type of substrate you use to line the tank bottom. It is important to thoroughly research the needs of your fish so you can choose a substrate that matches their requirements but still looks pleasant to you. Referencing this article will allow you to consider the important points associated with the selection of your aquarium’s substrate and lead you towards a choice that you and your fish can enjoy for years.