Increased rate of precipitation the higher pH climbs. This puts at risk all wet equipment. As far as how high before livestock becomes endangered, that's a good question.
Are you able to dose the Kalk at night when pH is lower, or perhaps dose smaller amounts more frequently?
Also you can add vinegar to the Kalk to reduce the increasing pH when dosed.
No discussion regarding effects above 8.5 and livestock, however a good read nonetheless:
http://www.reefkeeping.com/issues/2007-05/rhf/