The JBL ProAqua Test O2 Oxygen is designed for the measurement and routine control of the oxygen content in saltwater and freshwater aquariums and in mains water and garden ponds within the range of 1 - 10 mg/l (ppm). Precise indication of oxygen content in freshwater and marine aquariums as well as garden ponds.Why test? All animals living in water need oxygen to breathe. Even theinvisible helpersin aquariums and ponds, the cleansing bacteria, are dependent on a sufficient oxygen content for the conversion of ammonium to nitrate. The oxygen supply they need can be safeguarded by adequate planting. In aquariums and ponds with little or no planting and in marine aquariums, the oxygen content always needs to be kept at the appropriate saturation value with the help of technical equipment. The saturation value depends on the water temperature (see table on last page). Plants are able to exceed this saturation value through their assimilation activity. In well planted aquariums and pon