To reduce fading of the DAPI stain and maintain the filters on the microscope, always close the shutter between the mercury bulb and the filters when not viewing the oocyst.
Some analysts have noted that DAPI staining of Cryptosporidium usually is negative or positive with nuclei stained, whereas Giardia is often negative or positive with intense blue internal staining.
Use 400X magnification minimum for DAPI characterizations, preferably 1000X.