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’s copper 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.