Spouts of greenery through black soil - Photo by Markus Spiske.

DIY Substrate for Planted Aquariums: The First Muddy Steps

Unless you dump in your tank a single type of inert substrates like sand, gravel, volcanic rock, or pebbles, technically, any mixture is a DIY aquarium substrate.

But here I cover a few basic principles to follow when mixing substrates that involve dirt.

Topsoil is the most crucial element in any DIY planted aquarium. Plants can grow in inert substrates too, but for a heavily planted tank, the fertilization that stems from organic potting soil is invaluable. Just like anything living in your aquarium, topsoil comes with its quirks.

So, the DIY principles discussed below focus mostly on dirt, but they can be applied to commercial aqua soil setups, too.

The Principles of DIY Substrate for Planted Tanks

Dirt is the most accessible nutrient-rich substrate option for heavily planted tanks.

It can be free, it can be bought from the store. The latter will give you more consistent results over time as it would have a stable composition. Freely collected topsoil from the same area would also be largely the same, but weather phenomena can still change the composition of the dirt.

The most important consideration for topsoils is that they are organic. This means free of herbicides, pesticides, and chemical fertilizers. Many organic potting mixtures contain natural fertilizers like manure. In small amounts, it is safe to use in substrate mixes for plants and other livestock.

Another important characteristic of topsoil is that in aquariums it is very much bottom soil. It must be capped at least on top. Its spreading across the entire bottom could also be limited by artificial or natural barriers.

So, a DIY substrate should include:

  • Organic soil
  • Inert substrate to cap it off
  • Barriers to prevent unwanted substrate mixture

How to Prepare Soil for Dirted Aquarium

It may all look like mud to you, but soil can be washed. It may never become un-muddy, but that’s not the goal when preparing it for your aquarium.

  1. Collect soil. A molehill is a good source of relatively clean, rich soil.
  2. Sift through it. Here you can remove most stuff you may want removed: rocks, plastic, and rotting branches.
  3. Return worms, beetles, centipedes, and other little critters where you dug them from.
  4. Drop the topsoil in a bucket.
  5. Cover with water.
  6. Mix it well. This will give homogenous material to work with, producing more even results across the tank.
  7. Optional: Remove debris. See what floating stuff you want to throw or try to bury under the cap. 
  8. Rinse a couple of times.
  9. Optional: Let it dry. If you want to refine the dirt to the maximum, let it dry under the sun (or in an oven) and sift through it as much as desired. This process will reduce the need for water changes but won’t eliminate it. It will reduce the components in the soil that are yet to fully decay but won’t remove them entirely.
  10. Insert in the tank.
  11. If muddy, scape it as you wish.
  12. If dry, sprinkle with water, work it into mud, and shape it as you see fit. Soil soaked in water isn’t very good at keeping structures. If you want to scape a protrusion from the bottom, you will need some support or the mud will try to compact. Sideways.
  13. Cap it.
  14. Cover with several inches of water.
  15. Siphon debris.
  16. Let it rest overnight to compact.
  17. Fill up.

If it’s organic soil from the local plant nursery or the hardware store that you know from other hobbies like gardening, you may apply it directly to the bottom of the tank. In such cases, follow the above process from step 7 onward.

How to Set Up a Dirted Tank

The dirt must be at the bottom, sealed by inserts substrates like sand or gravel.

Cover all the areas of the tank you want with an inch of dirt and cover it from all sides but most crucially from the top. Cap it well, with a couple of inches of inert substrate. As you gain experience with planting root plants in a layered tank, you could reduce the cap accordingly.

Still, don’t go under one inch.

Uncapped dirt can onset a bunch of issues like algae blooms and ammonia spikes. Keeping all topsoil well sealed makes things much more controlled.

You can cover the entirety of the bottom, all but the corners, or certain spots. Restricting dirt from moving horizontally can be done with plastic forms or natural barriers like flat stones or gravel around the islands of soil.

So, here are the basic steps for preparing aquarium substrate by yourself:

  1. Procure topsoil and inert substrates
  2. Prepare them
  3. Apply the muddy dirt wherever you want at the bottom of the tank
  4. Shape it
  5. Cover it with a solid cap of inert substrate like sand or fine gravel (or both, if you dare)

To see how it is done in practice. I have no videos of my own but even if I had, they could never match the beautiful simplicity of the first video by GreenEcoSpace:

Here’s an inspiring aquascape made with DIY substrate by MadeByKM. The interesting part is that they use clay pebbles to prompt the garden soil to an impressive aquascape.

Can Aquarium Plants Live in Plain Sand or Gravel?

Sand and other inert substrates can certainly maintain plant life. They provide ample space for roots to spread and, gravel especially, retain more mulm. Over time, the biowaste of the aquarium seeps through the substrate layers, infusing them with plant nutrients.

Do Planted Aquariums Need Special Substrate

Plants can grow and, eventually, thrive in inert substrates. As long as there is biowaste produced by fish or snails, or food, the plants will be receiving nutrients from the water column. After a few months, the substrate will have enough aquarium soil, as in, soil produced within the aquarium.

The biowaste accumulation is akin to how terrestrial topsoil forms. Dead (or dying) organic matter falls down and decomposes. Decomposition is induced relatively slowly by decay or faster through digestive systems.

So, inert substrates can be enriched enough to maintain a dense plant mass.But it is fair to say that aquariums need special substrate mixtures to become lush and vibrant. Nutrient-rich soil is the special component that feeds the plants and helps them thrive. It is not the only prerequisite, but, together with adequate light, it is one of the main limiting factors of plant growth.

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