I have used CP to treat crypto with great success - 60mg/gal for active infections, 40mg/gal for general quarantine. I have treated clownfish, rabbitfish, chromis, basslets and firefish successfully. The only challenges I have come across have been Paracheilinus spp. (flasher) wrasses. They seem to tolerate CP for 3-4 days, then perish quickly thereafter.
If you are interested in giving CP a go, there's a lengthy thread in this forum with a great deal of information on it. CP is still not considered "mainstream" by many hobbyists, but it is used by public aquariums and is advocated by a number of fish disease specialists like Edward Noga and Bob Goemans. I prefer it to copper-based medications, as it is well-tolerated by fish in general and is a "one and done" medication.