Iodine boosts macroalgae and some kind of corals. At least the type of iodine I use to dose.
Some species use a lot more iodine than others, but I tested that hypothesis fairly carefully for Caulerpa racemosa and Chaetomorpha and didn't see a statistically different response with and without dosing. I show that study in this article:
Iodine in Reef Tanks 2: Effects on Macroalgae Growth
http://www.advancedaquarist.com/issu...l2003/chem.htm
from it:
What type of macroalgae did you see a response in? What form of iodine?