There are many types of aquarium substrate available nowadays with products ranging from neon-colored gravel to natural-looking sands. Substrates are an important place for beneficial bacteria to grow but choosing the right products can be a bit of a challenge, as each substrate type has a different effect in your aquarium and on your fish.
Keep reading for a list of the most common aquarium substrate types and their pros and cons, which will hopefully help make picking out the best substrate for your tank a bit easier!
There is more to aquarium substrate than meets the eye; while it certainly helps bring color and texture for a natural-looking tank, an appropriate substrate provides a place for bacteria to grow and fish to forage. As the water in a new tank cycle, the nitrogen cycle is being established. Waste in the form of ammonia–usually produced by fish later on in the life of the tank–enters the system and needs to be converted to nitrite and nitrate; otherwise, it can really hurt your fish, inverts, and plants! The bacteria required to complete this cycle use the surface area available in your tank to populate, which is largely made up by your substrate. This is why cycling new aquarium water can take so long: all that bacteria is slowly growing and filling up every space possible to keep up with the influx of ammonia and other nutrients.
The substrate can also make your fish feel more natural in their tank. A bare-bottom can create a reflection, possibly making your fish react to its own image in a bad way! This can cause your fish to become timid and force them to stay towards the back of the tank. Or, if your fish is an aggressive species, it could hurt itself trying to attack its own reflection. On top of this, many fish enjoy foraging the bottom of a tank for food and could even rely on it for safeguarding their eggs when they spawn.
Picking the right substrate is also very important if you plan on keeping plants. Certain plants do best in a coarse substrate while others do better in a fine substrate. There are also many products that contain extra nutrients to help your plants grow, but we will go over this further later.
Lastly, the substrate just seems to add something extra pleasing to look at in any tank and is often understated!
Types of substrate
We will discuss the most popular substrate products for fish and plants, including when best to use gravel or sand in your tank!
Fish tank gravel is probably the most commonly used aquarium substrate in the hobby. It’s available in many different particle shapes and sizes and is often dyed in bright artificial colors but also comes in natural tones. There is a type of gravel substrate for almost every setup, with a few exceptions depending on what fish, invertebrates, and plants you plan on keeping in your tank.
If you’re thinking of using gravel, really consider your stock first. Be sure to check which substrate the fish you’re interested in will do best on. Some species, like Corydoras catfish, like to sift through the substrate to find their food; gravel will make this quite difficult for them, and a sharp gravel substrate may even damage their delicate barbels and cause rot.
Other aquarium fish, like kuhli loaches, like to burrow into the substrate and have delicate bellies that could be damaged by sharp gravel. Using aquarium sand is not absolutely necessary for these fish, but it will allow them to display their natural foraging behaviors without getting hurt. One fish species that should never be kept on aquarium gravel is the ever-popular goldfish; gravel can get stuck in their throat and you could end up having to take it out with a pair of tweezers, which obviously causes the fish a lot of stress and could even prove to be fatal.
Another point to keep in mind if you’re considering aquarium gravel, especially bigger sizes, is the fact that dirt particles and uneaten foods will be quite difficult to remove from the tank. They can build up and cause bad water quality if the gravel substrate is disturbed after a long time. If you do decide to go with gravel products, especially with the fish species mentioned above, a smaller polished type of gravel is probably your best bet! Natural colors will be greatly appreciated by both your fish and the viewer and is less likely to leak out any unwanted dyes or chemicals into the water.
Although a sand substrate is not the first choice for most new fishkeepers, I personally prefer it. When used correctly, sand is a great substrate that causes little to no problems. Dirt particles tend to stay on top of it instead of getting buried, so cleaning your tank becomes much easier in the long run.
Slightly coarser sand products with a medium grain size like river sand work best, as they have a much smaller chance of becoming anaerobic and causing ammonia spikes if disturbed after a long time. Sand substrates with very small grain sizes, like play sand, should be avoided unless you’re only using a very thin layer! Using sand that is too fine is the reason many new fishkeepers have bad experiences with this type of substrate. It can become compacted and anaerobic and live plants will not be able to develop their root systems properly.
Live plants will do well in a sand substrate that has a larger grain size, and will also be appreciated by bottom-feeding fish like loaches, goldfish, and catfish. If you’re worried about your sand becoming anaerobic in your tank, be sure to disturb it once in a while during cleaning and avoid using a thick layer. Malaysian trumpet snails can also be of use for your tank; they burrow in the substrate, thereby disturbing it on a regular basis.
Crushed coral/aragonite substrate
Crushed corals and aragonite are substrate products that are not usually used in most aquarium setups. They harden the water and act as a pH buffer in the tank; the pH will be raised and stabilized without using any chemicals. This is not required and even unwanted in a regular tropical aquarium because most tropical fish need a lower pH.
However, if you’re interested in keeping African cichlids or a brackish aquarium, one of these substrates could help! Though crushed coral substrate products are traditionally recommended at many aquarium stores, the (slightly more expensive) aragonite seems to be preferred by most fishkeepers because crushed coral can trap dirt and can eventually cause problems with your water quality. You can buy aragonite online here.
Marbles, river rocks, and lava rock substrate
Bigger (decorative) rocks and marbles are sometimes used as a substrate by themselves. While these are all suitable for use in your aquarium, it may be best to just use them as decorations instead. Dirt can get trapped between rocks and marbles quite easily, and in some cases, a fish could even get stuck.
Smooth rocks and marbles are not a good place for beneficial bacteria to grow on. These rocks can, however, be scattered across the regular substrate for a decorative effect. Lava rock substrate would be great for beneficial bacteria but lava rock is better suited for use as the biological filter material inside your aquarium filter or as part of your hardscape.
Substrate for plants
If you’re interested in keeping live plants, you can consider substrate products that contain extra nutrients, like Eco-Complete, to help your plants grow. However, they are not absolutely necessary to achieve a lush green tank; most plants do just fine without a special substrate as long as water parameters are maintained.
While enriched substrate products can be used as a “main” substrate, there are also extra live plant nutrients that should be placed under your regular gravel or sand substrate, like laterite. These are not necessary for good plant growth either, but can definitely help make your tank a little lusher! Just be careful when planting, as you may accidentally stir up the laterite and cause your water to become cloudy.
Although using substrate has many advantages, there are a few situations where a “bare-bottom” aquarium is preferred. Many goldfish keepers choose not to use a substrate because this makes cleaning the tank much easier. Goldfish are very messy fish and with the number of water changes required, and a tank with no substrate may be even more convenient.
Keeping live plants is a challenge in a bare-bottom aquarium though, but with some creativity, it’s certainly possible. When you’re setting up a quarantine tank, breeding tank, or display tank, it’s also not necessary to add substrate as these are temporary holding places.
There are many substrate products out there, all with a specific use and aesthetic. While it is appealing to go with a cheaper substrate at first, your whole tank is literally built upon it; so keep that in mind as you go forward! Make sure to check which substrate is best for your fish, invertebrates, and plants, and also know what is involved in maintaining it before purchasing one.
If you have tips or questions about choosing a substrate, feel free to leave a comment below. Happy fishkeeping!