crisis cranks unscrewing themselves?

Pubert

hey all im having problems with the crisis cranks on my dmr rhythm. A while back the bearing in the bb got a bit mashed so i replaced them. This has now resulted in the cranks uncrewing themselves slowly as i ride. So every now and then i have to tighten them up which is getting annoying. the guy at my local bike shop did this for me but i think the bb is isis but im not sure what the bearing are.
any comments or suggestions would be appreicated. thanks

hugh