Picking The Right Substrate

Substrate is a fancy word for what you put at the bottom of your aquarium like gravel, sand, or rocks. Some substrates are great for fish-only aquariums while others have benefits to both fish and plants. The purposes of substrate are:

• It helps the fish orient up and down. Since the top surface is naturally reflective, having a reflective bottom surface  confuses the fish and stresses them.
• It’s a great breeding ground for needed bacteria and other organisms.
• It’s a natural habitat for crabs, sea snails, and other bottom dwellers.
• It provides a nutrient-rich layer for live plants and a place to anchor.
• It gives a natural look to your aquarium.

Selecting the right substrate will go a long way to helping you maintain your aquarium’s delicate ecosystem. This ecosystem is an artificially balanced and needs your intervention to make sure it stays balanced.

How Much Substrate Do You Need?

In general, having about 2-2.5 inches is enough. Having more than that and you run the risk of excess food particles getting trapped in the depths where there’s less oxygenation. Then the food particles degenerate into hydrogen sulfide which is not only high toxic to the fish, it smells like rotten eggs.

In order to estimate how much substrate you need, measure the surface area of your tank (in inches) and divide by 20 to give you the pounds. For example, if your tank is 15″ x 25″, you’d need approximately 18.75 lbs. of substrate.

Neutral pH Substrates

These substrates do not affect the water pH of your aquarium at all.

Gravel

This is them most common substrate and the type varies from very coarse to very fine. It’s mainly made of quartz and is only suitable for either fish-only aquariums or the top layer of a 2 layer substrate for live plants. Gravel needs regular vacuuming to remove food particles that slip into the crevices.

Sand

Avoid sea or ocean sand (i.e. going to the beach and scoopingup some sand). The sand tends to contain a wider variety of organisms that you want and when they die (and they will die since your aquarium will not have everything they need to survive), their bodies will decompose, producing ammonia and making your water more acidic. But with that said, sand can make an excellent substrate. It tends to compact to prevent food particles from lodging between grains and sand is a natural habitat for bottom dwellers. However, you will need a good filtration system to remove food particles from the surface or you will need to perform regular vacuuming. Two sources of cheap sand are:

• Sandblasting sand (which is coarser than regular sand)
• Play sand (used in playgrounds)

One advantage of play sand is that it is sterilized for the protection of children.

Substrates That Raise pH

The following substrates will release a steady stream of buffers that will reduce water acidity and raise pH levels.

Crushed Coral

This has been a traditional favorite of aquarium owners throughout the world. Often a crushed coral mix is comprised of calcium-rich minerals like dolomite, calcite, or argonite. Because of the calcium content, it will buffer well and will push your pH up to 7.6 or so. However, pure crushed coral is coarse and it tends to trap debris (food particles and fish waste material mostly) which will result in overall more nitrates. Nitrates are toxic to fish. Also, crushed coral will harden over the years and after years or decades, it will cement together, making removing a big hassle.

Argonite

Argonite is a calcium carbonate mineral which slowly releases its calcium carbonate, buffering the pH and raising it up to 8.2. The released calcium is valuable for live coral as a source of building material.

Living Plant Friendly Substrates

The following substrates tend towards neutral pH but have benefits especially for live plants in your aquarium.

Laterite

Laterite does not contain any nutrients but has the ability to store and release nutrients for plants. It tends to be porous and makes good lower substrate for live plant aquariums. The cheapest form of laterite is cat litter but often, cat litter contains perfumes to hide urine odors and clumping agents to make cleaning convenient. Aquarium-grade laterite is sterilized and does not contain any additives.

Vermiculate

Vermiculate is a magnesium, iron,and alumnum mineral mixture that absorbs and releases phospates over time. It also converts ammonia to nitrates. Both nitrate and phospates are nutrients to plants. Like laterite, it makes a good lower substrate for plants but its tendency to compact makes it less than ideal. However, a combination of laterite and vermiculate resolves these issues and makes an excellent lower substrate for plants.