This is a liquid test kit, which works by changing the colour of a pond water sample by addition of a liquid agent. The colour of the reultant mixture lets you know your pond ph \'score\' instantly. pH levels can be raised by increased levels of Carbon Dioxide in the water, normally as a result of the air, acidic rain, debris and by the lack of pond plants to soak up any residue toxins. When the levels get too high or too low, the fish and life inside the pond will suffer as they struggle to breath. The ideal level in a pond is 7.4 with the ideal level being 6.5 to 9.