How to Pick the Best Substrate for a Planted Aquarium

Welcome back to Part 3 of our Getting Started with Aquarium Plants series. Today’s article will explore the topic of tank substrates. Substrat is the “soil” or ground at the bottom of an aquarium. It is what many living plants require to grow roots and absorb nutrients. Interestingly, some aquarium plants (e.g., rhizome plants, floating plants, and most stem plants) prefer to absorb nutrients directly from the water, whereas others (e.g., sword plants, vallisneria, cryptocorynes, and certain carpeting plants) mostly feed from their roots. Your choice of substrate should be based on the type of plants you wish to keep.

Companies have spent a lot of time and research into developing plant-specific substrates to help plants grow well, but which kind is the best? This article gives a quick overview of all substrates to help you customize them for your particular needs.

Nutrient-Rich Substrates

Before aquascaping and planted tanks became popular, people used soil to grow their plants. Organic soil contains many essential nutrients for plants, and the texture closely matches the lake bottoms or riverbanks where plants are found in the wild. But what happens when you combine dirt with water? A big muddy mess. This can be fixed by covering the dirt with gravel or sand. It will prevent the dirt from clouding water. However, it is best to not move any plants. It is possible for soils to become depleted of nutrients over time, just as farming does. This means that the substrate must be renewed. You can either pull out the plants and let the “land” lay fallow while the fish waste reintroduces nutrients or you can remineralize the soil with root tabs and other fertilizers, but both methods tend to cause very murky water that is difficult to clear up.

Easy Root Tabs are made of nutrient-rich topsoil and clay to help grow plants that are heavy root feeders.

Due to the difficulty of maintaining dirty tanks, manufacturers developed specialized substrates for plants such as Aquavitro Aquasolum and ADA Aqua Soil. These compact, nutrient rich soil balls are sometimes called “active substrates”. Because they lower pH and soften the water hardness, many people use them in crystal shrimp tank and aquariums with large root-feeding plant populations. Substrates are mostly made from organic materials and can become very muddy over time. After one to two years of usage, these substrates also become exhausted of nutrients and will need to be remineralized like dirted tanks. Finally, nutrient-rich substrates are usually the most expensive option on the market, so if you are using plants that don’t primarily feed from their roots, there are more cost-effective alternatives.

Crystal shrimp tanks with large root feeders and planted aquariums that have a lot of fish are able to use nutrient-rich substates. However, they need to be replenished with new nutrients regularly and can break down over time.

Substrates inert

Unlike nutrient-rich substrates, inert substrates come with very few nutrients, which may sound bad at first but keep reading. It is possible to set up a tank with rainbow gravel purchased at a pet store and then later add plants. This is because most plants rely on the water column for their nutrition. Just regularly dose an all-in-one liquid fertilizer that contains most of the macronutrients and micronutrients your plants need. You can add a heavy root feeder, such as an Amazon blade, by inserting root tabs. This will convert your inert substrate and make it nutrient-rich.

Rhizome, floating, and stem plants primarily absorb nutrients directly from the water column, so keep them well-fed with a comprehensive fertilizer like Easy Green.

There are many brands available for planted tanks such as Seachem Flourite or CaribSea Eco-Complete. They are not like aquarium gravel and do not have to be replaced. These substrates, which are usually made from volcanic or clay-based gravel, have a higher CEC (cation exchange capacity). This simply means the materials are better at holding onto nutrients (such as from fish waste or fertilizers) so that plants can easily use them for greater growth. Inert materials don’t have an impact on the pH, water hardness, and other parameters of water in any significant way.

Although almost any substrate material is suitable for growing aquarium plants, it is important to limit the size of the substrate. Very fine sand is hard on plants because the particles are very small and tend to compact together, making it difficult for the roots to easily penetrate and spread through them. Coarse sand, however, creates small pockets between the particles and works much better as a planted tank substrate. If you go to the other extreme and use large river stones as your ground cover, there’s too much empty space between the substrate pieces, which makes it hard for rooted plants to grab onto and get well-established.

Regular gravel works well even with Amazon swords and other root-feeding plants, as long as you keep the substrate fertilized with root tabs.

Which Substrate is Best?

There is no single right answer. You cannot just look at an awesome aquascape and copy the substrate it uses because everyone’s water is slightly different. To test the nutrients in their soil, gardening enthusiasts are serious. You may need to amend the soil with dolomite, peat or other potting media based on the results. You may also find that your plants are lacking important nutrients like calcium and magnesium if you live near soft water. In order to compensate, your optimal substrate choice may actually be a mixture of Aqua Soil and Seachem Gray Coast, an aragonite-based substrate high in those missing ingredients. Ask other local plant tank enthusiasts for advice and to help you choose the right substrate.

Very few plants in this beautiful aquascape require substrate, so a cheap, natural-looking sand was used to cover the tank bottom.

The key point is that you don’t have to spend a lot of money on expensive substrates in order to get amazing results. Be strategic about the plants that you will be using and the specific needs of each plant. If you buy a lot of anubias, but only one root-feeding or heavy plant in your corner, mineralize the substrate and then fill in the tank with a less expensive option such as gravel. You don’t want to lower the pH or soften the water if you are making a tank for African cichlids.

We hope you found this article helpful in understanding the various types of planted tank substrates available and what ones best suit your needs.