Limestone gravel
Also known as: Crushed coral, Coral sand, Aragonite, Cichlid sand
Properties
| pH effect | raises pH |
|---|---|
| KH (carbonate hardness) | hardens |
| GH (general hardness) | hardens |
| Nutrient load | none |
| Ammonia release initially | No |
| Particle size | 1 to 5 mm |
| Longevity | indefinite |
| Cost tier | moderate |
How it affects the tank
- Continuously dissolves trace calcium carbonate, buffering pH upward (typically toward 7.8-8.4) and raising KH/GH
- Required for African Rift Valley cichlids (Mbuna, Tropheus) and many livebearers that need hard alkaline water
- Incompatible with soft-water species (tetras, discus, most South American cichlids) and acid-loving plants (most aquarium plants underperform above pH 7.8)
- Plant selection narrows considerably: only the hardiest plants (anubias, java fern, vallisneria, hornwort) tolerate the hardness
Care notes
Buffering capacity is finite: pure aragonite eventually dissolves down to less-soluble residue and stops affecting water chemistry. Replace or top up every few years. Mixing with inert sand (50/50) gives moderate buffering for soft-medium water targets.
Plants that work in limestone gravel
8 aquarium plants in the catalog list this substrate as compatible.
Sources
Data drawn from: seriously-fish, rift-valley-cichlid-keeping. Last verified 2026-05-13.
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