I will share my latest observations on knight tank class :
Even though i used Phirius Deposit-Injector(ID:1244820), I lose half of my mana after 30 seconds in combat as knight/druid. However, if i have a mana regenerating class in party such as druid/priest or druid/scout, i never have any mana problem (as it is supposed to be).
Classes like kinght/mage and knight/rogue will not have mana problem because of their mana recovering elite skills.
But at the moment playing knight/druid is really difficult.
My suggestion is that bring back mana recovery to Holy Power Explosion. Just remove mana recovery when receiving heal. It should recover 5% mana in 5 seconds as it was before.