Water testing equipment and meters measure water quality. Calibration solutions, such as buffer solutions, help keep pH constant when running biochemical assays. Chemical process controllers treat batches of incoming process water, rinse water treatment, recirculating system and wastewater treatment. Colorimeters test concentration levels of chemicals and heavy metals. Conductivity meters measure the capacity of ions to carry electrical currents in an aqueous solution. Dissolved oxygen meters measure the amount of gaseous oxygen in water. Electrodes and probes test water in the lab or the field for ions, solvents, pH, heavy metals, and sulfites. Hydrometers determine standard parameters and special applications for a wide range of liquids. ORP meters measure the cleanliness of water and its ability to break down contaminants. Salinity meters measure the amount of alkali metal salts or magnesium salts in aquaculture, aquariums, fish ponds, and in environmental treatment.