Magnesium Carbonate (Magnesite) is a slow-release, non-sulphate source of magnesium that doubles as a soil pH buffer — raising pH in much the same way as lime or oyster shell powder, but supplying magnesium instead of calcium. If you've used dolomite, you've used something similar — dolomite is calcium magnesium carbonate, while this is purely magnesium and carbon without calcium tagging along. That distinction lets you fine-tune your calcium-to-magnesium ratios with real precision, rather than being forced to add both every time you adjust pH.
Magnesium is critical to enzymatic processes throughout the plant's life cycle, and running short of it will affect overall performance drastically — particularly flower quality and yield. Because magnesium carbonate is insoluble and non-acidic, it fills a completely different role to ingredients like kieserite or soluble magnesium sulphate, providing a long-term background supply rather than a quick soluble hit.
