Alkalinity (carbonate hardness) measures the carbonate and bicarbonate that corals and calcareous algae need to build skeletal material, and it's a major factor in keeping pH stable in the natural 8.1-8.4 range. Natural seawater runs about 2.7 meq/L (~7.5 dKH), and a stable tank shouldn't drift more than about 5% (roughly 0.14 meq/L / 0.4 dKH) from its target. Resolution: 0.1 meq/L (0.3 dKH) steps, with a sharp color change Kit size: approximately 100-200 measurements Correcting alkalinity means adding back bicarbonate and carbonate without disturbing pH - a well-formulated buffer (like Salifert's KH+pH Buffer) settles to the tank's natural pH within about 24 hours. If pH stays low longer than that, weak gas exchange (insufficient aeration) is the usual cause.
