Substrate depth depends on tank type + plant or aesthetic goals. Fish-only freshwater: 1-2 inches of sand or fine gravel. Enough to look natural, easy to vacuum. Low-tech planted (anubias, java fern, crypts): 1.5-2 inches inert sand. Anubias + java fern attach to driftwood/rock anyway. High-tech planted (carpets, root feeders): 2-3 inches with aquasoil base + sand or gravel cap. Some scapes use 4-6 inches at the back to create slope. Reef tanks - shallow: 0.5-1 inch aragonite sand (CaribSea Special Grade, Fiji Pink). Easy to vacuum + high flow over substrate. Reef tanks - deep sand bed (DSB): 4-6 inches sugar-fine sand. Provides anaerobic denitrification at depth. Maintenance-intensive + crashes ugly if disturbed. Mostly out-of-favor for modern reef. Avoid the 2-3 inch reef trap: too deep for proper turnover, too shallow for anaerobic denitrification - anaerobic pockets release sulfide. Bare-bottom: SPS reef + breeder grow-outs. Pros: max waste removal, hot water flow. Cons: visually stark. Slope: shallow at front (1") + deep at back (3-4") for visual depth. Black diamond blasting sand is a budget alternative to expensive aquarium sand - inert, dark color, ~$15 per 50 lb at Tractor Supply.
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