If adds are killing your clerics, your OT's are not tagging them fast enough. We once had this problem, so we set up an OT at each of the 2 doorways where the adds come from. Whichever door add paths to, that OT grabs it and pulls it in. DPS just switch rooms depending which room the add pathed into.
As for prev. post, wow, I've never heard of clerics using a pause 25, how many clerics do you avg. on a raid? We avg 5-7 total, 2 of which we put on adds, leaving 5ish for main tank. We typically have a 5-man rot(4clr 1dru) at pause 8 or 12 on a 16-17k tank and do a tank-switch when each tank's evasive drops. And me being 5th clr on tank, I'm in the tank group patch healing/refreshing DI/rez/rebuff tanks if they die during fight. Adding me as an add-on cleric to the rotation improved our chances of success ten-fold.
Also, like raddude was saying, if you tanks cannot survive a CH rotation and/or adding on a patch cleric like I do, try using a 5 or so P. Remedy rotation on tank from 100-70%, at 70% do a tank switch toa tank that has fortitude (15sec parry disc) and do CH rotation from 70-0. Obviously it takes a cleric who can handle the switches.