Scrapes can only be taken from live koi,most parasites disappear from dead koi after about fifteen to twenty minutes,take the scrape from just below the dorsal fin ,inline with the pectoral and the tail,also the under belly,
when you have a smear of mucus on the centre of the slide use your cover glass to take a drop of pond water and place it over the mucus,
this will cause a river type affect on the outer rim of the slide,you will be able to see the likes of costia swimming against the currant,if the mucus is quite thick in some areas you will have to keep adjusting your magnification slightly,download some videos of koi parasites from youtube on to your desktop for reference.
