Alkalinity – Quick Reference

Alkalinity – Quick Reference

Alkalinity (kH) is also referred to as carbonate hardness. Alkalinity is a measure of the buffering capacity of water, or water’s capacity to resist changes in pH. Since most biochemical activity in aquariums results in more acid conditions, alkalinity tends to decrease. Total alkalinity is determined by the amount of free positively charged hydrogen atoms required to neutralize the negatively charged bicarbonate, carbonate, and borate ions present in a liter of aquarium water. When the positively charged ions are neutralized by organic acids, alkalinity drops. In reef systems, carbonate ions are required by coralline algae and hard corals to secrete new skeletal material. In the ocean, carbonate ions are constantly replenished and alkalinity remains fairly constant, but in a closed aquarium system, alkalinity must be adjusted.

Alkalinity is measured in meq/l (millequivalents per liter). One meq/l is equal to about 50ppm calcium carbonate(CaCO3). Test kits are labeled Carbonate Hardness, Alkalinity and kH. Test kits labeled Total Hardness or General Hardness are for freshwater hardness measurements only. The basic measure of carbonate hardness and alkalinity in saltwater and freshwater is in ppm. However, different countries may express this measurement in different units. Often products for freshwater are labeled kH or dKH – same test just in German units of degrees. The most common measurements are German dKH, ppm CaCO3, or meq/l.

Simply put, alkalinity is a measure of the buffering or pH stabilizing capacity of aquarium water. The higher the carbonate and bicarbonate concentration, the more stable the tank. Monitor alkalinity to maintain stable pH.

Freshwater –
3-7kH is favorable in most tanks. If kH is low and pH is unstable, increase kH. Heavy plant load requires kH adjustments. To raise alkalinity, water change and/or adjust with pH Stable for planted and fish only tanks.

Saltwater –
7-10dkH or 2.5-3.5 meq/l is ideal. To increase kH, water change and/or adjust with Reef Builder and/or SuperBuffer dkH.

1 meg/L = 50 ppm CaCO3
To convert meq/l to ppm CaCO3, multiply by 50
To convert meq/l to dKH mutiply by 2.8
To convert dkH to meq/l divide by 2.8
To convert dKH to ppm multiply by 17.9

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