Bentonite will cause a bit of constipation so YES too much is an issue.
Do you take fiber along? Liquid or the powder?
I used to take 3 tspoon a day (1tsponn 3x/d) with psyllium. BUT I slowly started with one/day and a laxative (senne, Epsom Salt or a salt flush) for the few days, then the bm adjust and become regular (consider angmenting the magnesium/ reducing according to the quantity of bm you get). I would progressively augment to 2 over a week and then to 3/d when I felt ready - chelation is a tricky - and demanding treatment - plenty of vitamin E and C. Ideally you should be followed - are you? or do you attend the Chelation Forum?
Taking papaya enzymes, bromelain or any other blend of digestive enzyme will help 'digest' candida in the bowels. Again, I did that with fiber along in the mix.