Aquarium Gravel Ratio to Tank Size

When you purchase an aquarium you will probably choose to place gravel in the bottom. Although gravel is not absolutely necessary, it serves more purposes than simple decoration. Gravel can be a key in establishing your aquarium's nitrogen cycle. When waste lands in the bottom of the tank, it settles down into the gravel. The gravel can eventually house bacteria that will break down waste and keep your fish healthier. Gravel serves as an anchor for plants, especially live plants whose roots can provide additional breakdown of waste products in the tank. Gravel can also add color and texture to otherwise blank glass surfaces.

  1. Selection

    • Once you have selected your fish tank, you need to choose your filtration system and other accessories. If you chose an undergravel filter you will absolutely need gravel. Gravel holds the filter in place and catches waste as the undergravel filter sucks water through the entire tank bottom. The gravel you select will need to be large enough to allow water to flow through it. You should choose a gravel that has been prepared for an aquarium. This helps to assure you that there are no latent toxins in the gravel that will harm your fish. You will still need to rinse the gravel in water before placing it in your tank.

    Ratio

    • If you chose to use gravel, and especially if you are using an undergravel filter, you need to know how much gravel to get. You will probably want 3 inches of gravel in the bottom of the tank. This works out to about 1 to 1 1/2 pounds per gallon. A 100-gallon tank would need 100 to 150 pounds of gravel.

    Second Method

    • Another way of computing gravel needed is to multiply the length times the width of the tank bottom. Multiply the result by 10 and round the number off by dropping the last digit. A 10-inch by 20-inch tank would give you 200, dropping the second zero gives you 20 pounds. This is the same number you get by estimating 1 pound per gallon, as these dimensions are those of a 20-gallon tank. You will have to account for variation, however, if you are filling a tank designated by the number of gallons followed by an H. This means the aquarium has been made to hold more water with a smaller footprint and it is designated H for "high," meaning the tank has higher sides and therefore a smaller bottom than others holding the same number of gallons.

    Set Up

    • Place your undergravel filter in the bottom of the aquarium. Attach the vertical pieces to the circular openings in the filter. Place these vertical tubes at the back of the tank so they don't detract from your view of the fish. Connect air tubes and air stones to the undergravel filter according to the instructions that come with the filter. As the air bubbles up through the vertical stack, it will pull water up with it. This forces water to flow through the gravel, then down into the filter.

    Add Gravel

    • Once you have the undergravel filter set up, you can begin working on the gravel. Place a small amount of gravel in a large spaghetti strainer in the kitchen sink. Run water over the gravel thoroughly until the water coming out the bottom of the strainer is clear. Dump the clean gravel into a bucket and carry it to the aquarium. Slowly scoop the wet gravel out of the bucket and into the aquarium. Spread the gravel out without shifting your undergravel filter setup. As you add layers of clean gravel, slope the gravel slightly higher at the back of the tank. This will give you a good view of all your fish and plants in action.

    Accessorize

    • Add any accessories you purchased for your tank at this point. Plants can be settled into the gravel. You may need larger rocks placed around the plants to hold them down until their roots establish. Add larger rocks, figurines and sculptural elements you purchased for the tank. When you have everything arranged, place a saucer in the bottom of the tank. Pour your water slowly into the tank, allowing it to hit the saucer. This prevents the water from destroying the arrangement you just made. If some of your decorative items start to float, reach in and turn them upside down to allow air bubbles to escape. Fill the tank to about 75 percent and then check to make sure the gravel is in place and all your accessories are where you want them.

    Further Set Up

    • Check your other aquarium accessories for instructions in setup. You may be installing a power filter, a heater, a lighted hood or other electrical items. Read safety instructions for using these electrical accessories in and near water. Check that all items are installed correctly in order to avoid splash, siphoning and electrical damage. If you have an air pump with plastic tubing, for example, pay attention to its placement because a power outage can allow water to siphon back through it if it is placed lower than the tank. Following product instructions can prevent damage and injury. Add water-conditioning chemicals and activate your tank. Check all systems and make sure that air is coming through your undergravel filter. Watch for bits of plant debris or other floating objects to check that water is flowing down into the gravel. Finish filling the tank.