I think you are going about this the wrong way. You really can't effectively copper treat fish in a tank with calcium rocks. The calcium will quickly take out the copper. As a matter of fact, you may have to add 10 times the recommended amount of Cuprimine or copper to get a cure. (but don't do that) Ich can be eradicated from any fish in about two and a half days with copper if you keep it at the correct level. A low dose of copper (or Cuprimine) will do nothing. My recomendation as was said is to remove any coral rock or sand and treat the tank with the correct dose. You have to check the dosage every day or even twice a day. Copper is a very potent poison for fish, inverts and paracites. Fortunately, fish have a greater capacity to deal with it, but not much. Paracites are inverts so copper kills both. Crabs can sometimes live especially hermit crabs.
Don't let the toxic effects of copper scare you into not using it. All good medications are poisonous in the wrong dose. Think Chemo or radiation, even aspirin will kill you is overdosed.
When I started with salt in the early seventees I continousely kept copper in my tank. In those days all fish had ich and since there was no reefs, the fish were never that healthy. My tank is still running with that same gravel.
Hypo will kill ich but not as fast as copper. As was also said, the copper may not kill the paracites on the fish but it makes the fish produce much more slime which is thought helps the fish eliminate the paracites so they can be killed by the copper.
I personally don't use Cuprimine, I use copper and formulin or copper and quinicrine hydrocloride which will get the ich off the fish in about a day. The quinicrine alone will sometimes work and it will not kill the snails or crabs or affect your bacteria. It is hard to get as it is a prescription drug for maleria.
Also copper will not kill your bacteria either.
Good luck.
Paul
