It looks like you're heading for a 5-day drop of about 150 which should be 95% of the phoretic mites = 160 phoretic mites in total. If this is 30% of the total population then you appear to have started out with a mite population of about 530, which is not too terrible although do not forget the immortal words of Finman "they will double in a month"!
CVB
500 ish mites is a heck of a lot for a "small nuc" to cope with, that's the problem, small nucs with a significant mite load struggle to build as so much of their brood gets damaged., control the mites and they can suddenly flourish.