Absolutely no chemicals are needed. Not even Iodine. When I first started propagating I would add Iodine to some water and let the shrooms 'marinate' in it for a few minutes before adding them back to the tank. Well, one day I didn't have any so I just added them right back. The shrooms recovered faster and grew fast without the iodine than they ever did with it. I tested it on a few more corals and got the same results. Several of these tests were side by side comparisons.
So basically the whole Iodine thing is a big load of bologna in my opinion. I have since fragged hundreds... prolly thousands of mushrooms and rarely ever loose any and have never (knock on wood) had any with infections or otherwise.
Basically if you have good water quality (Ca, Alk, Mg, salinity, ph) You should be able to frag away. Stay away from essential elements and all that other bull crap. It's useless money grubbing junk!