If you feel like using Fluid Aura for extra damage, make sure to position yourself so the mob is between you and a nearby wall (if any) so the target won't get knocked back far from the tank's range or on the one that's about to die. Bosses mostly have knockback immunity so feel free to use it when it's up for extra DPS. There are also plenty of other (situational) use like interrupting an enemy's cast.

And yeah, Quick Stoneskin is kinda pointless atm since it the cast time reduction is only half a second.