What sand should I use, and how much?
When: When aquascaping, before adding saltwater
Short answer: Place rock directly on the glass bottom before adding sand, then add a shallow bed (1-2 inches) of reef-grade sand — fine "sugar" sand is easiest for most tanks, while a coarser Special Grade (~1-2mm) holds up better under strong flow. Size the quantity with a sand-bed calculator for your tank's footprint rather than guessing.
The details
Sand isn't just cosmetic — it supports sand-sifting animals and adds a bit of biological filtration, but it also traps detritus, which is exactly why the corpus repeatedly recommends a shallow bed over a deep one: deep sand beds can develop pockets of trapped hydrogen sulfide that turn dangerous if the bed is ever disturbed (accidentally dug into, for example).
Grain size matters with flow: very fine "sugar" sand (~0.25-1mm) is the most common choice and looks natural, but it blows around in high-flow tanks; a coarser Special Grade Reef sand (~1-2mm) is specifically recommended for reef tanks running strong flow because it stays put. Live/pre-inoculated sand exists and carries a head start of bacteria, but it isn't required — dry sand cycles along with the rest of the tank.
Order matters: always place rock on the bare glass bottom first, then pour sand around and under it. Sand added first lets rock shift or settle unevenly later, which can crack glass or topple an aquascape.
Bare-bottom is a real alternative some reefers (often SPS-focused) choose instead of sand — easier cleaning, no detritus trap. The corpus notes it as an established option without laying out a full protocol, so treat the specifics as something to research further rather than a beginner default here.
The numbers
| Parameter | Guidance |
|---|---|
| Bed depth | 1-2 inches (shallow), not a deep sand bed |
| Grain size, most tanks | Fine "sugar" sand |
| Grain size, strong flow | Special Grade Reef (~1-2mm) |
| Rock placement | On glass, before sand |
| Quantity | Use a sand-bed calculator for your footprint |
Common mistakes
- Adding sand before rock. Rock can shift later and crack the glass.
- Going deep "for more filtration." A disturbed deep sand bed can release trapped hydrogen sulfide — shallow is the safer default.
- Fine sand in a high-flow tank. It blows into snow-drift piles; match grain size to your flow.
When to worry
- Normal: Sand shifting into small dunes near powerheads — just a flow/placement thing.
- Worry: Disturbing a long-undisturbed deep bed and noticing a strong rotten-egg smell — that's trapped hydrogen sulfide; ventilate and do a water change rather than stirring further.
What's next
Rock and sand chosen — put them together in how-to-aquascape-your-tank.
- A deep sand bed that gets disturbed (risk of trapped hydrogen sulfide)
- Reef Knowledge Base — Tank Setup & Cycling (sand)
- Reef Knowledge Base — Digging Deep into Sand: What YOU Need to Know About Substrate
- Reef Knowledge Base — Sand or Bare Bottom?
- Reef Knowledge Base — Aquarium Sand: Deep Sand Bed or Shallow? Coarse or Fine?