My only experience with Tsulong is LFR, but what I do is Flash Heal x2 (the 2nd one should hit right after Sun Breath is cast) -> Greater Heal -> Holy Word:Serenity -> Renew. Then don't heal Tsulong until your Renew has expired.
If you timed it right, you should be able to fit everything in a Sun Breath duration (you might be able to add another Flash Heal if you have time), and you can build up some crazy high Echo of Light ticks. I've seen 70k+, and I think I reached 100k once with Guardian Spirit on him. Casting any heals on Tsulong will greatly reduce the following Echo of Light ticks, and refreshing Renew by any means will replace the massively boosted heal. In LFR, I destroy the meters on this fight.
In the last Terrace LFR run I did, Tree form + Nature's Swiftness + Sun Breath + lucky crit = 3.2 million HP Healing Touch.