keeping a mandarin goby?

[fatman]

Start out with a good sized partial water change like 40%. There is an old saying, "The key to pollution is dilution." If you know how to use Kalkwasser and are not using it now would be a good time to use it. Kalkwasser causes dissipation of Copper. Cleaning your substrate with a vacuum will remove nearly all heavy metals being actively dissipated. Charcoal is good for removing a lot of different chemicals but it has to be replaced frequently when being used to remove known quantities of a substance as charcoal will leach chemicals when used for too long. Hopefully it was a chemical compound medication such as a stain or anti biotic or who knows what and not copper as copper will penetrate the surface of aragonite and carbonates real well, meaning your rock and substrate surface are impregnated with copper if you used copper any length of time ago and did not follow up with water changes and carbon etc. I believe this site has an article on removal of copper from reef rock (carbonate based rock).