Is there an amount of copper in a tank that inverts like shrimp and crabs can handle? I had to treat my tank with Copper Power for Velvet after Rally by Ruby Reef didn't do the job. I'm using both Cuprisorb and ChemiPure to remove the copper but after about two weeks still show about .5 on the tests. I was up to about 1.75 at one point before beginning the removal process. I realize I can never put corals into the tank now but can crabs, shrimp, and even possibly and anemone handle a particular amount?