I was reading the info on Kordon Novaqua+, and on their website, they claim that it breaks down copper in a way that makes the copper harmless to inverts. I've been doing all of my waterchanges using Novaqua+. So, I am thinking copper shouldn't be an issue anymore. Here is the paragraph from their website(they don't sell from their website-it is info only).
One of the most toxic of heavy metals to fishes is copper, a common ingredient in tap water. NovAqua+ is capable per dose of precipitating up to 1.17 ppm free copper ions (Cu++) from solution. When copper is present in the tap water or when copper medications are used, the copper ions can combine with glass, plastic, rock, gravel, and other objects and remain indefinitely in this state. Variations in pH (acidity/alkalinity) may cause the copper to come back into solution and be toxic to fishes and invertebrates. NovAqua+ permanently detoxifies copper and can be used to eliminate copper ion medications after their use as a treatment is completed.