i'm not sure if it is a valid strat for other tanking classes, but we let our feral tank take stacks early on (he was in the 2nd group) because he can deal insane damage in this fight somehow.

interrupts: install ora and display interrupt cooldowns. let the people with short cooldowns (< 15s) do the most, and those with long cooldowns should save them up for crucial situations like getting the water puddle buff (we found it easier to just spread and move to get the buff, instead of stacking up on top of the boss because the waterbolt damage would hit everyone every time) or when a corrupted water is up. make sure your positioning is so that it allows melees to always be in combat range.