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. The type of plants that you choose to keep will also affect the substrate selection.

Research and companies have spent much time developing substrates for plants that are plant-specific. But what kind of substrate is best? This article provides a high-level overview of substrates so that you can customize them for your needs, so let’s start by talking about the two main types: nutrient-rich and inert substrates.

Nutrient-Rich Substrates

Before the hobby of planted tanks and aquascaping became more well-known, people took a cue from mother nature and used soil to grow 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 do you get when you mix dirt with water? A big muddy mess. The majority of people solve this problem by sealing or capping the dirt. This prevents the dirt and water from clouding the water. This works well as long as the plants are not moved. The soil can also become depleted in nutrients, as it happens with farming. Therefore, the substrate needs to be rehabilitated. 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 from nutrient-rich clay and topsoil to aid in the growth of plants that are heavy feeders.

Because of the difficulties that come with maintaining dirted tanks, manufacturers created specialized plant substrates such as ADA Aqua Soil and Aquavitro Aquasolum. These soil-like, compacted, nutrients-rich balls are known as “active substrates”. They lower pH and soften water hardness and are used in aquariums that have heavy root-feeding plants and crystal shrimp tanks. The substrates are made primarily of organic materials so they can break down and become muddy just like regular dirt. These substrates will also lose their nutrients after one to two years of use and will need to remineralized as if they were in a tank of dirt. Nutrient-rich substrates are often the most expensive on the market. If you don’t have plants that primarily feed off their roots, there may be more affordable options.

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.

Inert Substrates

Inert substrates have very little nutrients. This is a big difference from nutrient rich substrates. But don’t worry, it won’t sound so bad. 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 of inert substrates for plants, including Seachem Flourite and CaribSea Eco-Complete. Like aquarium gravel, they do not tend to break down over time and therefore do not need to be replaced over time. This substrate is made of volcanic and clay-based gravels that have a higher cation Exchange Capacity (CEC) than regular aquarium gravel. 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.

While almost any substrate material can be used to grow aquarium plants, remember to avoid the extremes when it comes to substrate size. Because the particles of fine sand are small and compacted together, it is difficult for roots to penetrate and spread through. Fine sand is able to create small pockets between particles and can be used as a substrate for a plant tank. 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 is compatible with Amazon swords, root-feeding plants, and other species as long you keep the substrate nourished with root tabs.

Which Substrate is Best?

There is no single right answer. It is impossible to simply look at an amazing aquascape and duplicate the substrate because every person’s water has its own unique characteristics. For example, in the world of gardening, serious hobbyists test their soil to find out what nutrients they have and which ones are missing. The results may indicate that you need to amend your soil with peat, dolomite or another potting medium. You may also find that your plants are lacking important nutrients like calcium and magnesium if you live near soft water. Aqua Soil mixed with Seachem Gray Coast is a good choice. It’s an aragonite substrate rich in these missing ingredients. Therefore, talk to other local planted tank enthusiasts who have similar water composition, and try different substrates and substrate mixes to find out what works best for you.

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. Instead, be strategic about which plants you’re going to be using and what they specifically need. 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. If you’re making a planted tank for African cichlids, the last thing you want to do is lower the pH and soften the water, so don’t pick nutrient-rich substrates if possible.

Hopefully, this article has given you a good overview on planted tank substrates and which types are most suited for your particular needs.