Either your tank forgot shield oath / Defaince, or you are overhealing too much, which will also cause MP problem in the latter.

As whm, you should know how much damage is coming, and how much healing you can put through per spell.

For example
Geocrush, 1 medica2 is enough to top people to full as long as they are not near center.
2 Tumult : 1 medica is enough, and 1 medica 2 is over heal => means 4 Tumult = 1 medica2 + 1 medica 1.

Just make sure, that if there is no incoming damage, you don't need to be hurry.