Phosphates in a tank is not good for coral growth and it promotes nuisance algae and cyno bacteria. IMO flow does not have much to do with coralline algae, I have it in high and low flow areas. Keeping you calcium and alkalinity levels up where they should be will help growth. Never heard of iodine having anything to do with CA, what ever you decide to use NEVER put additives in before testing for them first.
There are plenty of posts on coralline algae on the site, do a search for it..
coralline is hard, cyno bacteria is soft.