Substrate Guide — Gravel vs Sand vs Soil: Which is Best?

Substrate is more than decoration. It affects your water chemistry, plant growth, fish behavior, and how easy your tank is to clean. Here's a complete breakdown of every substrate type and which one is right for your setup.

Gravel: the classic choice

Gravel (2-5mm size) is the most common substrate. Pros: easy to clean, available everywhere, cheap, won't cloud water. Cons: no nutrients for plants, some fish (cories, loaches) prefer softer substrate. Use gravel for: fish-only tanks, beginners, setups with fake plants.

Sand: natural and fish-friendly

Pool filter sand or aquarium sand mimics the natural environment of most tropical fish. Pros: looks natural, cories and loaches love it (they sift through it), easier to spot leftover food. Cons: can compact and develop anaerobic pockets without disturbance, requires gentle gravel vacuum. Use fine-grained play sand (NOT beach sand) for the most natural look.

Planted substrate: nutrient-rich soil

For planted tanks, a nutrient-rich substrate is a game-changer. Fluval Stratum, CaribSea Eco-Complete, and ADA Aquasoil all contain iron, minerals, and organic matter that feed plant roots directly. No extra fertilizer needed for months. They also lower and buffer pH, which most tropical plants and fish prefer.

How deep should substrate be?

Fish-only tank: 1-2 inches of gravel. Plant tank: 2-3 inches minimum (plant roots need depth). Iwagumi/aquascape: often sloped, deeper in the back (4+ inches) and shallower in front (1 inch) to create perspective. More depth = more planting options.