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Asked by akmoline ·September 12, 2018 ·13.7k readers

Coral sand

If using purchased coral sand calcium carbonate for WCA is it necessary to toast before mixing with vinegar?

coral-sand growth-stage spraying nutritive-cycle

The answer

Drake Weinert Foundation · Sep 13, 2018 ✓ Marked as the answer
Yes, it is still important to toast coral sand. The reason for toasting to a light brown like a perfectly done marshmallow is twofold:
  1. Remove the moisture from the calcarb so the vinegar will penetrate more easily and thoroughly dissolve all the calcium out into solution
  2. Coral is full of tiny bits of organic matter, so to cook them out so that the mixture will not rot later during storage.
I recommend doing this on a slightly higher heat that has been traditionally taught, around a low medium so that it will take about 15 minutes with constant stirring as not to burn. Try not to burn the coral and turn it black as that chemically destroys the calcium and starts to carbonize it. Sort of like the marshmallow, it takes keen effort and the right heat to cook it just perfectly! Good luck, and Long live the natural farmer!

From the KNF library

From the KNF library Drafted by Claude from Office Hours and the books · Sep 2026 · 4 sources

The library backs the accepted answer and adds a ratio, a dissolve time, and a split on heat.

The Pure KNF Manual lists crushed coral beside eggshells and seashells, and says to toast it first. (Pure KNF Manual, p. 51) KNF Demystified says commercial calcium carbonate, such as crushed coral, can be used for larger batches. (KNF Demystified, p. 40)

  • The recipe ratio is 1 part toasted material to 10 parts brown rice vinegar by weight. That recipe is written for eggshells. (Cho's Solutions, p. 13)
  • Dissolve for 7 days with a breathable lid. (Cho's Solutions, p. 13)
  • Another source says to wait until the bubbling stops. (KNF Demystified, p. 40)

The sources disagree on heat. The manual says to cook it "on relatively low heat". (Pure KNF Manual, p. 51) KNF Demystified gives about a half hour on low heat. (KNF Demystified, p. 40) The Cho's Solutions slides give 45 minutes on low heat. (Cho's Solutions, p. 13) An office hours summary of Master Cho's method says high heat. (Office Hours Ep. 154, 20:29)

The library gives no toasting time or heat setting written for coral sand itself.

Sources

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