I don't believe you have an iodine issue with your tank. Any good synthetic sea salt should contain iodine as well as all of the other important elements; so if your doing consistent water changes you should be covered there. Your specific gravity does seem to be high IMO. Most of the literature I've read suggests invertabrates seem to prefer the specific gravity close to that of natural seawater (1.026). However, most reefers who follow this practice usually go a step below and maintain specific gravity at 1.025. Also, keep in mind that if your testing your SG with a hydrometer, your SG may actually be higher than 1.027. If your salinity is to high, the shrooms may be working overtime to expel the excess salt. I would recommend you have a LFS test your water with a refractometer if you don't already have one. Don't know what type of filtration you have on your tank, however, it is speculated that mushroom anenomes may actually utilize dissolved organics as a source of nourishment. I have heard overskimming tanks full of soft corals can cause them to wither and eventually disappear. Doesn't sound like lighting could be the source of your problem, as mushroom anenomes, other than the ricordeas, aren't known to be highly dependant on lighting. I would just check all parameters (ammonia, nitrite, PH, phospates, etc) and maybe run some carbon just in case you have unknowingly introduced some sort of toxin into the tank. I'm definitly not assuming that you don't already know all of this stuff, however, I just wanted to make sure I gave you a thorough answer incase you didn't.
