How to Pick the Best Substrate for a Planted Aquarium

Welcome back to Part 3 our Getting Started with Aquarium Plants Series. In today’s article, we dive deeper into the topic of planted tank substrates. Substrate refers to the soil or ground that is placed at the bottom and used by live plants to absorb nutrients and grow roots. Surprisingly, some aquarium plants (e.g. floating plants, rhizome and most stem) prefer to absorb nutrients from the water. While others (e.g. vallisneria and cryptocorynes), mostly feed from their roots, other plants (e.g. sword plants and vallisneria) tend to take nutrients directly from the water. Therefore, the kind of plants you want to keep should affect your substrate choice.

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 popularity of aquascaping and planting tanks, people relied on soil to grow plants. Organic soil contains essential nutrients for plants and its texture is very similar to riverbanks or lakes where plants can be found in the wild. What happens when dirt is mixed with water? A big muddy mess. You can fix this by covering or sealing the dirt with gravel or dirt to keep the water from becoming cloudy. This works well as long as no plants are moved. As with farming, soils can become depleted of nutrients. The substrate must therefore be revitalized. 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.

Due to the difficulty of maintaining deep-water tanks, manufacturers developed specialized substrates for plants such as Aquavitro Aquasolum and ADA Aqua Soil. 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. Substrates are mostly made from organic materials and can become very muddy over time. These substrates become depleted of nutrients after about one to two year of regular use. They will 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.

Inert Substrates

Inert substrates contain very little nutrients. You can set up your first aquarium with rainbow gravel, but decide later to add plants. Because they mostly feed from the water column, this will work fine. 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 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. These substrates are often made of volcanic or clay gravel which has a higher cation-exchange capacity (CEC). 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.

You can grow aquarium plants with almost any type of substrate material. However, you should avoid extremes in terms of substrate size. Fine sand can be hard for plants as the small particles tend to form a compact, making it difficult to spread roots through. However, coarse sand creates smaller pockets between the particles, and is better for use as a tank substrate. You can also use large river stones for your ground cover. However, this leaves too much space between the pieces of the substrate, making it difficult for roots to grasp onto and establish themselves.

Regular gravel is good for Amazon swords and root-feeding plants. As long as root tabs are used, the substrate will work well.

Which Substrate Do You Choose?

Unfortunately, there is no one right answer. You cannot just look at an awesome aquascape and copy the substrate it uses because everyone’s water is slightly different. In the world of gardening, hobbyists can test their soil to determine what nutrients are present and which ones they lack. Based on your results, you might need to amend soil by adding peat, dolomite, or other potting materials. 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. You can talk to other people who have similar water requirements and experiment with different substrates and mix-ups to discover the one that works best for them.

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

Another key takeaway is that spending a ton of money on the most expensive substrate won’t automatically get you amazing results. You should be careful about what plants you choose to use and what they need. 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. When you make a plant tank for African Cichlids, you don’t want the pH to drop or the water to soften.

Hopefully this article will give you a solid overview of plant tank substrates and which ones are most suitable for your specific needs.