Free Chlorine - is the portion of total chlorine that is not combined chlorine and is available as disinfectant.
Combined Chlorine - is the chemical species that forms when chlorine chemically bonds to nitrogen-containing compounds like urine, perspiration, dead algae, ect. Combined chlorine can cause eye and skin irritation and has a strong chlorine like odor.
PH - is the negative logarithm of the hydrogen-ion concentration of a water solution. A measure of the degree of acidity or alkalinity of a solution. A PH below 7.0 is considered acid. A PH is considered alkaline.
Total Alkalinity - is a measure of the ability of the water to maintain a desirable PH when acid is added to the water.
Calcium Hardness - is the calcium portion of the total hardness. The level of calcium determines whether water is overly "soft" or "hard".
Cyanuric Acid - is a chemical that reduces the loss of chlorine due to ultraviolet rays from sunlight.