When Keeping Freshwater Fish And Plants, The General Hardness Gh And Carbonate Hardness Kh Of Aquarium Water Should Match Their Natural Habitat. The Api Gh & Kh Test Kit Helps You Duplicate The Natural Habitat Of Your Fish To Prevent Stress, Keeping Them Healthy Carbonate Hardness, Also Known As Alkalinity, Is The Measure Of Carbonate And Bicarbonate Concentrations Dissolved In Water. These Minerals Are Present In Municipal, Well, And Bottled Water. The Level Of Carbonate Hardness In Tap And Bottled Water Depends On The Source Of The Water And The Treatment Processes It Has Undergone. Carbonate Hardness Helps Stabilize Ph In The Aquarium. An Aquarium With A Low Kh Level Will Tend To Be Acidic. Aquariums With Very Low Kh Are Subject To Rapid Ph Shifts If Not Monitored Carefully. Water With A High Kh Level Usually Has A High Ph. General Hardness Is The Measure Of Calcium And Magnesium Ion Concentrations Dissolved In Water. These Minerals Are Present In Municipal, Well, And Bottled Spring Water. The Level Of General Hardness In Tap And Bottled Water Depends On The Source Of The Water And The Treatment Processes It Has Undergone. Hard Water Is High In Calcium And Magnesium, While Soft Water Is Low In These Minerals. Set Contains: 1 x API Aquarium Freshwater GH & KH Test Kit Contains 2 Test Bottles, Easy To Ready Instructions, And Glass Test Tubes Safety Information Please Read Instructions Before Use Directions Please click the Link: https://apifishcare.com/pdfs/products-us/gh-kh-test-kit/api-gh-&-kh-test-kit-instruction-manual.pdf