How to heal Tanks...

[Hanayome]

Medica II is great to use in response to multiple or back-to-back party-wide AoEs since the regen ticks can usually top off your DPS without having to use any direct heal spells/abilities.

I'd try and save it for AoE damage situations when possible. Its an additional regen you can throw out on top of your regen, asylum, etc. if you're really struggling with keeping the tank alive, just keep in mind that its also one of, if not THE highest MP consumer(s) out of your spells. If everything is going right, however, Medica II should not be necessary for most trash pulls. That being said, if your tank is making your life miserable, you can throw it out and use WHM's many MP-restoring abilities to cope with the higher mana usage.