Aquarium substrate is the layer to cover the bottom of a fish tank. It can be gravel, sand, crushed coral, or other forms of substances. While it is not mandatory, it is nice to have for the following reasons. First, some shy fish might be under stress in a bare bottom fish tank. Stressed fish will have weakened immune system, which may cause the fish to become sick. By adding aquarium substrate, you can provide a more natural environment to the fish. Second, by having substrate in the aquarium, it makes the aquarium look so much nicer. Third, in case you’d like to add some plants or other decoration, aquarium substrate can help to hold them in place better and distribute the weight more evenly across the bottom of the fish tank.

What Type of Aquarium Substrate Should I Use?

There are many types of aquarium substrates on the market, which make it difficult for some fish keepers to make a decision.

First, you should not get sand or soil from random places. It can contain unexpected pesticide and some chemicals harmful to the aquarium fish. Even sand from a seemly clean river might carry unwanted parasites. The fine particles of sand might even clog the filter in an aquarium. Regular soil can also make a mess in your aquarium by clouding the aquarium water. Therefore, we recommend using the commercially available alternatives as they are safe and easy to use.

Second, to choose a substrate for your fish tank, you must look at what type of aquarium you have.
For ordinary freshwater home aquariums without live plants or bottom feeders, any aquarium substrate available at pet shops will do. Regular fish tank gravel will work just fine, and it is the cheapest. You may choose any color you like. I recommend small sized gravel as it will make less room for the fish poop to get through, and it is easier to clean with an aquarium vacuum.

Bottom feeders such as Corydoras catfish like to dig around. The finer substrate of even smaller size is recommended for not letting the food slip through. You must also avoid getting the type of substrate with sharp edges since it might injure the bottom feeders’ mouths and their scaleless bodies. Sand is preferred by the catfish, but you should not use it unless you protect your filter intake with a pre-filter to prevent take in the sand. Live plants will also do better with smaller particle substrate because they can root better, but sand is too compact for them to root. It is also important to note that special substrate rich in minerals is essential for planted aquariums.  Because plants can’t thrive without all the needed minerals.

My personal favorite substrate for a planted aquarium is Eco-complete. It has a perfect size and shapes for both bottom feeders and live plants. There are more than 25 essential minerals in it.  Such as iron, magnesium, calcium, etc., for optimal plant health. It also has some natural bacteria to help break down fish poop to plant food, as well as to aid the aquarium nitrogen cycle. You have black and red colors to choose from. The red substrate is richer in iron.

How much substrates do I need in my aquarium?

For regular aquarium gravel, usually 1” deep is enough. You may add more according to your personal preference and the size of the fish tank.

For planted substrate, you will need a minimum of 2” for the plants to root properly. A layer of 2.5~3.5” is recommended if you have taller plant species. Research the individual plant species before getting the substrate is a great idea.

Since all the aquarium substrates manufacturers sell them by weight, it can be hard to measure how much of it you actually need. The general estimation is you need minimal one pound of the substrate for every gallon of water if the aquarium is not for live plants. For planted aquariums, you will need 2 pounds of the substrate for every gallon.

How Do I Add Substrate to My Aquarium?

You need to add the substrate before having any fish. Adding substrate to a fish tank should be a part of the aquarium setup. No fish should be added until everything is set up and running, as well as after a fishless cycling is completed.

To add substrate, you need no water in the fish tank. Carefully arrange the substrate across the entire bottom of the fish tank. More substrate should be at the back of the fish tank to create a slope for a better view. (Remember, you need to plant the taller plants in the back of the aquarium. And the lower plants in the front). Otherwise, you will just block your view. After all the substrate is in place, you may put a large plate on the top of the substrate before pouring water into the fish tank. The plate is there to avoid making a mess of the substrate when water is pouring into the tank.  

To summarize, we recommend regular gravel as aquarium substrate when you have no live plants nor bottom feeders. Eco-complete is a preferred substrate for a planted aquarium as well as aquariums with bottom feeders such as Corydoras catfish.