Why would you spec healing tide on this fight of all things?
Ancestral Guidance does 40% of your damage as healing, on a fight that increases your damage by 50% + However many stacks you get on the boss (Should be able to get at least 10 = 150% More damage) Why wouldn't you take advantage of the amount of healing you can put out with all your burst cooldowns up. In addition to the healing you can get in the last phase, you can also use it during the transition phase when the adds spawn, chain lightning cleave + ancestral guidance will 100% heal everyone to full HP.
Take a look at this log:
http://www.worldoflogs.com/reports/r...?s=5025&e=5060
I'm Enhancement and I did 1.9m Healing in the final phase, and our elemental shaman did 2.2m healing.
Our Elemental shaman didn't use his Ancestral Guidance as much as I did, but over that entire fight I was able to do 6.3m healing through it.
You didn't specify whether or not you were 10 or 25 man (Probably 10), but ancestral guidance is still just as effective in a 10 man setting as it is in a 25 man setting.