A Deeper Dive into Discus Tank Substrates

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A Deeper Dive into Discus Tank Substrates

The substrate (a surface on which an organism grows or is attached) in your planted aquarium is a critical part of your aquarium’s ecosystem and vital to the health of your plants. When planning your substrate, keep the following in mind.
  • Your substrate should not be too large or too small. Between three and eight millimeters is best. If your grains are too small, they will suffocate and crush the roots. If your grains are too large, there will not be enough contact with the roots.
  • Your substrate should not negatively affect your water chemistry. Make sure your substrate will not leech minerals and salts into the water. Because many substrates are designed for other uses, including salt water use, you should verify that it is safe to use the substrate in your discus aquarium. 
The depth of your substrate needs to be deep enough for the roots of your plants, but not so deep that it takes over your tank. Two or three inches is a good rule of thumb. If your substrate is too shallow, your roots will not be able to go deep enough to root your plants. On the other hand, if your substrate is too deep, that is unnecessary.



The following substrates are made specifically for planted aquariums.

Inert Gravel

Regular inert gravel can make a good substrate when used properly. When starting from scratch, you will need to be aggressive in your fertilization to maintain more demanding plants. You also want to make sure the size of the gravel is small enough to allow plant roots to take hold. Gravel that comes from an established tank can be used to start a new tank. It is a good choice because fish mulm, which acts as a fertilizer, is already present.


This substrate should be used with caution. While it is very attractive, there are several downsides. It can compact, which will make it difficult for roots to grow into it. If the sand compacts, water circulation is reduced and pockets of anaerobic bacteria can develop. If this happens, toxic gas bubbles are created. If you are going to use sand, it is best to layer another type of substrate underneath the sand or use very large grain sand. For best results, though, it would be best to only use sand in an accent area (like a sandy beach area), not for growing plants.


This is a very popular substrate well-suited for fish aquariums. It already has beneficial bacteria, you don’t need to rinse it, and it has the nutrients and minerals that are essential for live plants. The grain sizes are just right for optimal root growth, and it looks like deep, black, sandy gravel. The gravel is also rounded, so your bottom feeding fish will not be hurt.



This substrate has been around for a long time and is tried and true. It is a clay-based substrate and has a reddish color because of the high iron content. Before you put it in your aquarium, you need to rinse it thoroughly. The grains are large, so it is not suitable for plants with small, delicate roots. It also does not have as many minerals or nutrients as other available substrates.

ADA Aquasoil

A variety of these substrates are based on biotopes from around the world, including Amazonia, Malaya, and Africana. Each one has different colors and properties that are meant to simulate the biotope for which each is named. This substrate has round grains, allowing water to circulate, which helps to prevent plant roots from suffocating. You can also purchase a powdered version of this substrate that you can use as your top level to give your substrate a more aesthetic appearance. This substrate can also be a passive filter because it captures floating particles. It will maintain its shape for a long time and will improve nutrients needed by root feeders.
Using regular potting soil can be a challenge, but it can be an effective substrate if done correctly. It requires very little maintenance or fertilizing, and it grows plants very well. However, if you do not use this substrate properly, many disastrous problems can arise. If you are thinking about using soil as a substrate, you will want to read Diana Walstad’s book Ecology of the Planted Aquarium and check on planted aquarium forums for the best way to handle this type of substrate.



There are also a couple of substrates to avoid. These substrates include:
Red Sea FloraBase
This substrate is great for about a year, but then it goes downhill. The label will even tell you it needs to be replaced every year. Once its year is up, the granules start
to lose their shape and turn to mush. Furthermore, the only way to replace the substrate is to totally take down your tank.


Laterite (Cat Litter)

This should not be used as a substrate, but it can be used as an additive to your substrate. It is a form of clay that contains iron and acts as a sponge that stores nutrients. However, because it is clay, it will soften into a mud-like substance, and it would cloud your tank when it is disturbed. 


  • Which substrate will you use in your discus aquarium?
  • Which substrates will help nourish your plants?
  • What size substrate is best for your aquarium?

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