PH

From ReefPedia

Basically, pH is a measure to determine if a solution is either a base (pH more than 7), acid (pH lower than 7), or neutral (pH IS 7). For the most part, we are constantly trying to keep are PH between 8.3-8.5 and for the most part, the Alkalinity keeps it stable. pH is measured on a logorythmic scale, meaning 6.0 is 100x as acidic as 7.0. Carbon Dioxide will lower pH if enough is present, this will only cause a slight dip in pH overnight. The best times to test pH are before the lights go on in the morning, and right before they go off that evening. Thus you can see how your pH changes due to photosynthesis. Alkalinity or Carbonate Hardness (KH) Stabalizes pH, bicarbonate (HCO3-)& carbonate (CO32-) neutralize acids in the water. KH is measured in dKH or degrees of hardness. It is also expressed in meq/l or milli-equivalents per liter.