i have also read that iodine does promote growth, but the standard way to achieve this is to add iodine supplements. get an iodine test kit, and buy something such as kent marine iodine, and dose as directed until you reach the recommended level for your tank. this is only necessary if you have a lot of soft corals though, particularly xenia. for most applications, fi you just have a couple shrooms, the iodine replaced with regular water changes should be enough for the mushrooms to thrive.
I dose because i am trying to propogate shrooms and my single ricordia. this is not a necessity though from all of my research u8nless you are really trying to get maximum growth. again this can only be achieved safely with a test kit, overdosing can be a lethal problem.