Use Curaga as a panic-button only. Your tank will need to be ready to lose hate when you do and you will need to be ready to guard like hell.

Focus on single cures when desperate, or even better - use sacrifice since it grants regen, which is brilliant on a tank. Additionally, if you've got a good tank, only one character will be taking the bulk of the damage anyway, meaning no need for the multi-targeting spell.

And tell your tank off if he isn't using second wind to keep his own HP up a bit. Healing is not JUST the conjurer's responsibility.