For calcium, I'm now using CaribSea Aragonite Aquarium Reef Sand I purchased from a pet store.
They use it for saltwater aquariums and I'm not running my aquarium now. So why not use it.
Aragonite is the most soluble form of calcium carbonate. It doesn't have nitrogen or phosphorus.
Outdoors, I normally just use less expensive Dolomitic Limestone purchased from a garden center.
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