I wouldn't suggest using straight +20 Expertise gems. I'd ask for your armory but it's down now but I'd probably suggest taking out the 3 purple gems and replacing them with the +10 Expertise +15 Stamina gems which I believe are called Guardian's Dreadstone or something like that.
And if you do want to replace the Enduring Eye of Zul gems that you are using you could use Vivid Eye of Zul gems which are +10 Hit Rating and +15 Stamina.
I would strongly recommend never using any hybrid gem that does not include stamina in it for your regular tanking set. Avoidance sets and block sets are different of course but as far as your generic tanking set or you effect health set always make sure all of your gems have Stamina in there somewhere.