How much aquarium substrate do I need?

Buy by depth, not by guess. Decide how deep the floor should be, then convert that to pounds.

Pick a depth

• Sand: 1–2 inches. Deeper sand packs tight and traps gas.
• Gravel for plants: 2–3 inches, more at the back.
• Aragonite for reef: 1–2 inches; 3 inches for digging cichlids.

The quick rule

A common rule of thumb is about one pound of substrate per gallon of tank for each inch of depth. A 20-gallon tank with 2 inches of gravel needs around 40 lb — two 20 lb bags.

Bag sizes

Aqua Natural sands, gravels and aragonite come in 10 lb and 20 lb bags, many also as a 4-pack of 10 lb. Iwagumi sand and pebble come in 7.7 lb bags; bio-substrates in 5 lb wet bags.

Sloping the floor

Slope the substrate from front to back. It adds depth to the view and gives rooted plants more room where they grow tallest.