Balling is a method of elemental supplementation (CA,KH,MAG)for the sole purpose of growth/health.... its something like what a calcium reactor will do whereas ZEOvit is basically a complete system by which we have the added benefit of being able to "tune" the coral colouration to our liking.
So to compare them both is like comparing honeydew and watermelons.... Why i choose this 2 fruits.... Because they both are from the melon family...Like ZEOvit and Balling... Both is used for the benefit of the SPS its just that one has extra benefits.
Its true that balling gives better control over those 3 elements because thats what they are designed to do... whereas ZEOvit is mainly used to tweak colouration and they do not have any supplement solely for those 3 elements.(CA,KH,MAG). However ZEOvit does have a product to put in the calcium reactor(aragonite).
Hope this helps...I am in no way reprsenting ZEOvit of balling method.... Just an passerby very singaporean opinion.