How to Pick the Best Substrate for a Planted Aquarium

Welcome back to Part 3 in 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. Some aquarium plants (e.g. floating and rhizome) prefer to absorb nutrients directly from water, while others (e.g. vallisneria and cryptocorynes) prefer to feed from their roots. Therefore, the kind of plants you want to keep should affect your substrate choice.

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 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 popularity of aquascaping and planting tanks, people relied on soil to grow plants. Organic soil is rich in essential nutrients and has a texture that closely matches riverbanks or lake bottoms where plants can be found in the wild. But what happens when you combine dirt with water? A big muddy mess. Most people fix this by capping or sealing the dirt under a layer of gravel or sand to prevent the dirt from clouding the water, which works okay as long as you never move any of the 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 contain nutrient rich topsoil, clay, and other ingredients to support the growth of heavy root 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 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. 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.

Substrates that are inert

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. If you buy rainbow gravel at the pet shop and later decide to add plants, it should work fine for most stem, floating, or rhizome plants. They primarily feed from the water column. You can just regularly apply a liquid fertilizer that includes all the micronutrients and macronutrients your plants require. 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.

The water column is where the majority of nutrients are absorbed by stem, floating, or rhizome plants. Therefore, Easy Green can be used to provide a complete fertilizer for these plants.

There are many brands available for planted tanks such as Seachem Flourite or 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. Plus, as inert materials, they do not impact the pH, water hardness, or other water parameters in any significant amount.

While almost any substrate material can be used to grow aquarium plants, remember to avoid the extremes when it comes to substrate size. 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 use large river rocks as your ground covering, it will leave too much space between each piece of substrate. This makes it difficult for rooted plants and makes it more difficult to grab onto the surface.

Regular Gravel works well with Amazon swords or other root-feeding plants as long as the substrate is kept fertilized with root tabs.

Which Substrate is Best?

Unfortunately, there is no one 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. In the world of gardening, hobbyists can test their soil to determine what nutrients are present and which ones they lack. You may need to amend the soil with dolomite, peat or other potting media based on the results. In the same way, if you live in a region with soft water and then use ADA Aqua Soil that further softens your water, your plants may be lacking key nutrients such as calcium, magnesium, and manganese. 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 require substrate in this beautiful aquascape, so a low-cost, natural-looking sand used to cover the tank base.

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’re buying mostly anubias and only have one heavy root-feeding plant in the corner, save your money by mineralizing the substrate right around it and then fill in the rest of the tank with a cheaper option like 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.

This article should have given you an overview of the different types of substrates for planted tanks and which ones are best suited to your specific needs.