How do you reduce copper in an aquarium. Also, are there testing kits for it? I haven't found any.
The first answerer gave you what I use for testing copper. If you're having trouble finding the test, try fish stores that do a good volume of their sales in saltwater fish. I don't know why that's the case, because copper is used to treat freshwater parasites as well, and the effectiveness of the treatment is related to the concentration in the water (not how much you add to the tank, because copper will bind to organics). I'll also vouch for That Pet Place. I've done business with them for several years, and have never had any problems ordering from them and their representatives are helpful and actually know what they're talking about. For removing copper, I'd recommend one of two products. Activated carbon will remove copper (why you need to take carbon out when using copper-based medications) or using polyfilter in your filter. This works like a deionizer or activated carbon, but the media changes color to indicate what substances are being removed. This is good for diagnosisng mystery ailments, especially if the usual suspects (ammonia, nitrite, nitrate, and pH) can be ruled out. It comes in two sizes a 4 x8 pad for smaller hang-on filters, and a 12 x 12 pad for canisters. I was a bit skeptical of these when I first heard of them, but after checking out some third party tests and trying them myself, I have to say they work! A bit on the high-priced side for everyday filtration if you don't need them.
A comapny called Seachem makes a filtration product called Cuprisorb which is excellent at removing copper from water especially after the use of a copper based medication
