General Hardness or gH is the measure of calcium (Ca++) and magnesium ions (Mg++) dissolved in water. General Hardness is measured with the gH Test Kit. Carbonate Hardness, also known as kH, refers to the concentration of bicarbonate (HCO3-) and carbonate (CO3–) dissolved in water. Carbonate Hardness is measured with the kH Test Kit. Popular aquatic plants such as glosso stigma, riccia fluitans, hemianthus callitrichoides, rotala sp., ludwigia arcuata, etc., likes soft-water condition which have water chemistry to have 4 degrees of kH and 4 degrees of gH.
A lot of my customers are having problems determining the gH (general hardness) of their water using API gH test kit. Testing is easy if the test kit is not yet expired. The manufacturing lot number of the test kit is printed on the top of the bottle just over the label and the last 4 numbers will be the month and year it was bottled. If it’s over 2 years or so, it is expired and colors do not develop properly.
Watch the video below to see the actual how gH test kit changes from orange to green. Note how they placed the test tubes on a white piece of tissue to make it easier to determine the color. It will also be easy for you to see the right color under white light condition. The first part is testing kH. Fast forward to 2:00 to watch testing of gH.
Special thanks to asiandude666 youtube video.