No such thing as using to much mana unless you run out. Gotta do what gotta do to keep the team pew pewing.

Using to much mana is more an indication of the group not knowing the fight and taking damage in excess. I.E. Standing front of a sister or not moving out of tornado or migrating to and from*middle during phase changes.

Of course if you're just excessively casting succor for mitigation at wrong times or forgetting to keep eatherflow on cd during the intense periods that can be a problem too.