The API Copper Test Kit allows you to easily and accurately monitor copper levels to maintain copper-based fish treatments at therapeutic levels and tests copper levels from 0 to 4 ppm. The kit measures both free and chelated copper and is for use in both fresh or saltwater aquariums and ponds. Copper is a treatment used for many parasitic infections, and its levels must be monitored in an aquarium or a pond. The copper level can drop too low for the treatment to be effective, or can increase to a point that is detrimental to fish health.