Iodine is good for inverts, however, dosing once a month is definitely not a good idea - iodine is not that stable and you'll lose all of it in a week or two. Dose once a week or even once a day. Also, iodine-rich food such as Hikari crab cuisine is even better - my Amanos would kill for it.
I don't specifically buy food that contains significant amounts of iodine. They seem to get their share of whatever trace elements they need from anything they consume including algae and fish food.
The Iodine supplement and special "invertabrate food" are just myths and make you spend money that you really don't have to spend.
Iodine rich foods that I have been feeding to my exploding population of Cherry Shrimp are spinch and mustard greens. Both are quickly microwaved to soften. I find within 10 min of feeding the foodstuffs are covered with shimp gouging themselves. I feed heavy too. In my own mind I think that shrimp pellets that I also feed my fish would be high in iodine as it's made from shrimp and shellfish are natrurally high in iodine.
