Zeovit rocks is to remove phosphates and nitrates in the tank water. Totally different application from activated carbon.
By the way, if the main ingredient is zeolite as stated, there are many other brands in the market that also use zeolites as the main component and are much cheaper.
Anyway, information on the Zeovit system from the manufacturer:
http://www.korallen-zucht.de/files/zeoguide_english_1_03.pdf
And you can read their recommendation on using activated carbon for reef tanks on page 14.