How to Use Pea Stone as Aquarium Gravel

Pea gravel as an aquarium substrate has the "Goldilocks" factor going for it: You're looking for pebbles that are not too large and not too small. The right size of gravel encourages the growth of beneficial bacteria that eat fish waste -- a critical factor in the long-term success of an aquarium. For most aquariums, pea stone is an ideal substrate.

  1. Benefits of Pea Stone

    • The size of pea gravel's particles offers several benefits. First, it is big enough to let water flow among the pieces. This prevents the growth of anaerobic bacteria. In substrates with smaller particles, the flow of water can get blocked, leading to oxygen-free pockets. In these pockets, anaerobic bacteria can thrive and produce toxic compounds. At the same time, typical bean-size pea gravel or pea stone compacts just well enough that it doesn't create "traps" of free space where fish food can get trapped and rot, fouling the water. Such traps are more common with larger rock that doesn't compact as closely.

    Pounds Per Gallon

    • Several guidelines exist for how much gravel to buy. One holds that you want to purchase 1.5 pounds to 2 pounds of gravel per gallon of aquarium volume. For most aquariums, this generates a layer of gravel about 2 inches deep. This depth gives you enough gravel to run an undergravel filter or plant aquarium plants. For aquariums over 55 gallons, you should double the amount of gravel for gallons, since 2 inches of gravel will appear shallow in a large aquarium. This guideline does not require a lot of math, making it easy to use. However, since this guideline does not take into account the shape of an aquarium, it may not work well in unusually shaped aquariums, particularly very wide ones.

    By Area

    • You can calculate the amount of gravel you need by the footprint of the area you need to cover. This guideline requires more math but makes it easier to know exactly how much gravel you need. With this formula, you'll start by finding the area of the aquarium's footprint. Just multiply the width and the length of the tank. This will give you the square dimension of the aquarium's footprint. If you add 20 pounds of gravel per square foot of aquarium footprint, you will get about 2 inches of gravel depth. Keep in mind with any guideline, you should always round up; it's better to have extra gravel than too little.

    When Not to Use

    • In a few situations, pea gravel may not be the best substrate for your aquarium. If you have burrowing and bottom-feeding species, sand can make a better substrate. Pea gravel can injure and damage such species. They'll eliminate the risk of oxygen-free zones with their sand-sifty ways. If you intend to keep live aquarium plants, factor in the different substrate preferences that various plants have. For example, some species prefer soil or sand for their roots and cannot thrive in pea gravel.