Hardness Test Kits measure the alkalinity or carbonate hardness (KH) levels in the water.
Several types of water hardness tests are available: KH: GH (general hardness); and combined KH and GH kits.
API CARBONATE HARDNESS TEST KIT Aquarium Water Tes...
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API GH & KH TEST KIT Freshwater Aquarium Water Tes...
Salifert Carbonate Hardness & Alkalinity (Kh/Alk) ...
sera gH-Test 15 ml, 0.5 fl.oz. Aquarium Test Kits