Erm... I think there's no secret to it. Chance, perhaps? I've always been a semi-lazy reefer, so not very consistent in water changes, checking perimeters and maintaining them.
If you're talking about the above mentioned yumas, ever since I've shifted them to the corner (less light but same flow), they seem to be doing better. I think it was wilson's tank that experienced yumas opening up bigger than usual after installing the scrubber? I think that plays a part too for my tank.
I do dose Marine Snow and trace elements on a weekly basis.