SUCCESS! Was finally able to beat him today by standing still. There was a few things that made the difference without any nature resist:

- stand still and spread out
- power word:shield the whole party before the elemental spawns
- SPAM prayer of healing (better range than holy nova, and hits tank as well)
- make sure to pick up the elemental aggro
- make sure to pick up the colossus aggro after the merge

That being said, I lost my healer way before the elemental merged back to the colossus for the first time. I have no idea how I was able to last the rest of the fight without dying, but I just barely got him down. Better strategy would make this much smoother.

I went on to take Gal'darah down first time with everyone still alive - and got my first heroic down!! Feels so good. Thanks for all the tips.

For those that don't use shamans, this is how I did it (a very lucky kill given that my healer went down early): http://www.youtube.com/watch?v=CVHMf2Dne5M (video just uploaded - may still be blurry)