Our cleaner shrimp which has been in the aquarium for about 2 months has developed black spots on its body. Is this a sign that it is beginning to molt? Could it be a sign that water parameters are off? I did the full range of tests this AM and all seem fine with the exception of nitrate which is about 25 ppm. In addition to an Aqua Remora skimmer we run a Fluval cannister filter. We also have approx 55 lbs of live rock in a 46 gallon set-up. I thought I had read that the media in a cannister could actually harbor nitrate. Is this so? We run the Fluval as a "crutch" in case we do not keep everything in tip-top shape. The Fluval contains spong, carbon and bio media. I am also working on the calcium which is up to 360 and the alkalinity which is 3.5. Thanks for any help.