I can't find a MSDS, so I'm relying upon what I've read in a couple of threads about Cuprazin. Ingredients are Copper sulfate, Formaldehyde and Malachite green. The only one of those three that is useful for treating
marine ich is Copper sulfate, and that is comparable to what is in chelated copper (i.e. Coppersafe here in the states.) Therefore, the therapeutic range would be 1.5-2.0 mg/L or ppm for 30 days, and you would need a “total copper test kit” such as API’s to measure Cuprazin.
However, I strongly advise
against leaving a fish in formaldehyde (harsh chemical that is also a known carcinogen) for 30 days. Therefore, I advise you to run carbon/do WCs to remove all the Cuprazin from the water and use this instead:
Seachem Cupramine Copper Aquarium medication - 250ml: Amazon.co.uk: Pet Supplies
I also suggest picking up one of these so you can properly test the concentration of Cupramine periodically:
http://www.charterhouse-aquatics.co.uk/seachem-multitest-copper-test-kit-p-1373.html
You probably know better places/websites in the UK to order these products from.