I have a 30 gallon system with a mix reef and I use iodine. I use brightwells lugols iodine solution. I put a drop every other day. Everything looks good to me, but maybe it just makes me feel better. You gotta be extremely careful using iodine though, just slightly od and you could nuke the tank. You're supposed to test iodine before adding it to be safe, but I didn't. Really risky I know, but I underdose. I figure a little is better than none. Been doing it about a year now. Just be careful is all I'm saying, but try it. See how it works for you.