After doing some research on a 35 hex, they have plenty of floor space for a pair of kribs. I thought they were smaller.
Remember kribs can be very aggressive when breeding.....or they might not. It's a chance you'll be taking.
I had a pair in my 55 for awhile and they got along great with everybody. In fact they were my favorite fish, but they were young and didn't breed. After doing a bunch of research I was sorry I bought them because they could be so unpredictable, but at that point they were part of the tank and I would deal with it when they decided to breed. It looked like they were getting ready. The female claimed a cave and the male was guarding the entrance. Everything seemed to be going good.
One morning my male turned up dead for unknown reasons. The next week so did the female. I found nothing wrong and I haven't had any other issues since.
Anyway, I was afraid of the unpredictability of a breeding pair of kribs and the safety of my other fish if their aggression came out. I feel the Rams are just as interesting, stay smaller and are less aggressive.