Check the listing for details. Copper (Cu) Test Kit - Elos. Condition: New. Listed at 21.99 USD. The ELOS Copper Test Kit combines ease-of-use, with laboratory-grade precision. It can be used to detect copper or to measure residual copper levels before and after using copper cures in fish-only aquariums. Also, great for testing tap or source water for copper. Due to a number of stress factors that include poor water quality, unsuitable or fluctuating temperature or salinity, etc. etc., beginners and advanced aquarists can experience outbreaks of parasitic diseases such as white spot (Cryptocaryn irritans ), Velvet disease, (Amyloodinium ocellatum) and more. Treatment with Copper is often the only way to cure infected fish and prevent future outbreaks of diseases. However, copper concentrations higher than therapeutic values can be toxic to fish. Natural sea water contains about 0.003 mg/L copper. Although, it is a good treatment for fish parasites, Copper is very toxic to invertebrates. In freshwater, copper is less critical, but should be less than 0.05 mg/L. Listing and template services provided by inkFrog