This copper test kit worked well when I had a bout of ichthyophthyriasis that I needed to treat in my 55 gallon aquarium - I used Mardel Coppersafe (now from Fritz Aquatics resold) . I had no problem discerning the copper level when looking down through the tube after placing it on a light-colored surface (a sheet of paper works well). I will say that this kit did NOT work with the cordon copper remedy I originally bought from Petco, but since I had to buy Mardel to get rid of ichthyosis I think it was probably something with that drug. , and I was afraid of an overdose, tk. the instruction and the copper content of the test system did not match even remotely. It is generally recommended when treating your aquarium with a copper-based drug. As a side note, my aquarium is planted, has a corridor of black fins and both are unaffected.
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