How to Pick the Best Substrate for a Planted Aquarium

We are back with Part 3 of the Getting Started with Aquarium Plants series. Today’s article will explore the topic of tank substrates. Substrate is the substrate, or the “soil,” at the bottom and which many plants use 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.

Many companies have invested a lot of research and time into creating plant-specific substrates that will help plants thrive. But which type 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 aquascaping and planted tanks became popular, people used soil to grow their 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. 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. Also, soils eventually become depleted of nutrients (as it does with farming), which means the substrate must be reinvigorated somehow. 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.

Manufacturers created specialized substrates to help with the maintenance of dirty tanks. These compact, nutrient-rich balls of soil are also known as “active substrates” because they tend to lower pH and soften water hardness, so many people use them in crystal shrimp tanks and aquariums with heavy root-feeding plants. Substrates are mostly made from organic materials and can become very muddy over time. These substrates become depleted of nutrients after one- to two years of regular use. They will then need to be remineralized just like Dirt 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 inert

Unlike nutrient-rich substrates, inert substrates come with very few nutrients, which may sound bad at first but keep reading. 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.

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. They are not like aquarium gravel and do not have to be replaced. 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. They are also inert and do not have any impact on pH, water hardness or other parameters.

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 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. In the world of gardening, hobbyists can test their soil to determine what nutrients are present and which ones they lack. The results may indicate that you need to amend your soil with peat, dolomite or another potting medium. 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. 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 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. You should be careful about what plants you choose to use and what their needs are. 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. You don’t want to lower the pH or soften the water if you are making a tank for African cichlids.

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