Photo by Amy Woodward on Unsplash

DIY Sand and Gravel Substrate: Mixed Tank Setup

Sand and gravel are the most popular substrates in the fishkeeping hobby. Beautiful and affordable, each one is a great choice in its own right.

But what about mixing sand and gravel in the same fish tank? What if some fish prefer it sandy, others stoney? Can you create beauty with both substrates?

You can definitely combine gravel and sand substrates. There are two ways to do that:

  • Layers — When the entire bottom plane is covered in one type of substrate and then covered completely by another type.
  • Zones — Half-tank gravel, half-tank sand? Sure. Or a sandy island amidst the gravel sea? Also possible. With natural separators like rocks or driftwood, you can create visually stunning aquariums. Plastic separators also work great.

I would advise against mixing sand and gravel because that diminishes the visual appeal of each and can create a very dense substrate. When you have gravel, sand, and water mixed together, you are one step away from mixing cement.

So, here’s how you can go about a DIY sand and gravel aquarium bottom:

Materials You’ll Need:

  1. Gravel — Choose a size of gravel that suits your aesthetic preferences and the needs of your aquarium inhabitants. Avoid sharp-edged gravel that could potentially harm fish or damage their delicate fins.
  2. Sand — Opt for fine-grain sand that complements the gravel and creates a pleasing contrast. Make sure the sand is aquarium-safe and doesn’t contain any harmful contaminants. Playsand and pool filter sand are good options.
  3. Buckets — To wash and carry sand and gravel separately.
  4. Dividers — If you want to create zones in your fish tank, you’ll have to plan for ornamentals that will separate gravel from sand. Cutting the desired separator from a plastic bottle also works well.

Steps to Set up Sand and Gravel Tank:

  1. Prepare the Tank:
  • Empty the tank of water and decorations.
  • Clean the tank thoroughly to remove any residues.
  1. Prepare the Substrates:
  • Rinse each substrate individually and thoroughly, using a bucket or a sift under running water.
  1. Add the Substrate:
  • For layering, start with the sand. The gravel will settle into the sand ever so slightly, but if you put gravel first, a lot of the sand will just fill in the cracks.
  • Zones provide ample opportunities for aesthetic arrangements. Separate the gravel from the sand using flat stones, driftwood, or plastic cutouts. The latter can be stuck to the aquarium walls for firmer separation and support for more complex structures atop.
  1. Shape and Contour:
  • Use your hands or a tool to sculpt the substrate into desired shapes, hills, and planting areas. With plastic dividers, you can create support walls, build slopes, and hills.
  1. Add Water Slowly:
  • Fill the tank slowly with water. Pour water onto a plate or saucer placed on the substrate to prevent disturbing what you worked so hard to create.
  1. Planting:
  • You can add plant live plants immediately after setting up a tank. They help with cycling it and establishing it for more complex life forms.
  • You can plant with minimal to no water in the tank. If you are still feeling your way around the hobby, pour water halfway or more, to see how the plants actually look. 
  • Use tweezers or planting tools to insert plants into the substrate.
  1. Cycling:
  • Allow your tank to cycle for a few weeks before adding fish. This gives beneficial bacteria time to establish and create a stable ecosystem.
  1. Monitor and Maintain:
  • Regularly test water parameters and monitor plant growth.
  • Early on, regular water changes add valuable nutrients to the water column, helping plant growth.
  • Water changes help clear out the cloudy water typical for many new tanks.
  • Trim and maintain plants as needed. However, a sand and gravel tank without fish won’t generate many nutrients for the plants. Once fish food comes into play and fish start pooping around, plants will feel better. Over time, the substrate will accumulate an array of anaerobic life forms and will become a nutritive soil for plants to grow.
  • Liquid fertilization or root tabs will help plants establish and cover the aquarium early on.
  1. Vacuuming and Cleaning:
  • During regular aquarium maintenance, gently vacuum the surface of the substrate to remove debris and waste. Gravel and sand follow slightly different cleaning routines, though, which can complicate things a bit. Gravel needs more in-depth vacuuming as mulm and waste sift through its larger particles. Here are a few practical tips for gravel vacuuming.
  • Sand keeps most of the waste on top so vacuuming its surface usually cleans things off well enough.

Making Your Own Substrates for Planted Aquariums

The general principles of mixing two substrates apply not only to sand and gravel. Layering and zoning (and rinsing, for the most part) apply to all kinds of substrates.  Now, topsoil must be always capped but it also can be zoned across the bottom.

Aquasoils can be layered, zoned, capped, or uncapped. The most nutritious aquasoils usually are made of baked dirt or nutrient-rich topsoil. They can be used sparingly to boost plant growth or generously by the more experienced hobbyists.

Gravel and sand substrate mix is good for plants. Over time, with enough biowaste from fish, shrimp, and decaying plant matter, it will become excellent, even. But early on, the inert substrates don’t service plants much beyond anchoring. Fish food and fish waste enrich the water column and most plants will grow. But for them to thrive quickly, you will need the appropriate light and liquid fertilizer or root tabs. Fish tanks and specialized planted aquariums have slightly divergent requirements, especially early on.

One of the biggest advantages of gravel or sand is their inertness which makes them much easier to keep than any organic soil. Both dirt and specialized aquarium soils actively affect water chemistry. Dealing with them requires experience and investment of effort in the form of adequate maintenance. In the case of commercially sold soils, the investment is also monetary.

Gravel and sand also need maintenance, but the variables fishkeepers should monitor are significantly reduced. Mixing them adds some complexity to the maintenance routine, but it is still pretty straightforward to establish a stable water column. With patience, the inert substrates will start supporting more and more plants, and root tabs are a safer, more controlled way to kickstart lush growth compared to aquasoil or topsoil.

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