How to Pick the Best Substrate for a Planted Aquarium

Welcome back to Part 3 in our Getting Started with Aquarium Plants series. In today’s article, we dive deeper into the topic of planted 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, such as rhizome, floating, and most stem, prefer to take nutrients from the water. Others, like vallisnerias, cryptocorynes and sword plants, prefer to feed 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 will give you a basic overview of the different types of substrates, so that it is possible to customize them to your specific needs. Let’s begin by focusing on 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 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 are made from nutrient-rich clay and topsoil to aid in the growth of plants that are heavy 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 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. However, given that the substrates are primarily made of organic materials, they break down over time and become very muddy 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.

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. For example, if you set up your first tank with rainbow gravel from the pet store but later on decide you want to add plants, it will work just fine for most stem, floating, and rhizome plants because they mainly feed from the water column. You can just regularly apply a liquid fertilizer that includes all the micronutrients and macronutrients your plants require. To convert an inert substrate to a nutrient rich substrate, insert root tabs if you are adding a heavy root feeder such as an Amazon sword.

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. 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. 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 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 not one right answer. Because everyone’s water is different, you cannot simply copy an aquascape. For example, in the world of gardening, serious hobbyists test their soil to find out what nutrients they have and which ones are missing. Based on the results, you may need to amend your soil by adding dolomite, peat, or other potting media. 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. Your best substrate mix may be Aqua Soil and Seachem Gray Coast. This is an aragonite-based substrate that contains the 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.

One important point to remember is that not spending a lot on the best substrate will guarantee you incredible 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.

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.