Copper exists in water as a soluble salt or as suspended solids. Concentrations exceeding 0.1 mg/L are useful for controlling algae and plankton growth. Quantities ranging from 0.02 to 0.1 mg/L are toxic for some fish, so its use for treating fish disease requires careful monitoring. With Hach Water Quality Test Strips, technicians in the field can test many samples in only a few minutes, and make immediate evaluations on-site. No measuring, set-up, clean-up, or chemical handling are necessary. Hach test strips are also used in laboratories all over the world for pre-test screening-to detect the presence of materials that might interfere with lab testing.