How to: Iodine dip

Okay, dipped for 20 minutes in 50 gallons worth of iodine diluted into 1 gallon water... The spaghetti worms are still all over them. Is there any other way to get rid of these guys or should I do another dip tomorrow? Stronger concentration? Longer time?
A rock with a colony of zoas on it. Green and red ones. Don't know what they are called. There are a bunch of spaghetti worms that live between the polyps and lately they've been staying closed a lot because the worms seem to be irritating them.