Dr Holmes Farley has opined that iodine, in it's many forms, does not really do anything. He used to dose it and quit and never noticed anything. That being said, if you dose the right kind in the right concentration, then you cannot probably hurt anything... just get a test kit. You will get some anecdotal posts that iodine helped some folks and plenty more that it did not do much - however, you really need to find out what kind that they dosed because some kinds get skimmed right away, others bound to organics and never used and other kinds will float around for possible use.
http://www.advancedaquarist.com/2003/3/chemistry
Just changing a bit more water will bring this back to normal. It will also reload your iron which the chaeto probably depleted a bit.
The sweet spot for SPS is NSW parameters, IMO. I know that some folks like to raise nutrients, but I get the absolutely best color out of .01N and .005P, or very close to natural seawater. I would never let my P get over .01.
Like I have kinda posted before, you are going to need to pick a method and go with with. If you want to go pure Berlin, then stop dosing stuff, change your water and let the tank be and bring that fuge back online to get those nutrients down. If you want to go Zeo and add in nutrients and also carbon, then go full scale and do it 100%. Nobody can really ride two horses with one arse. I am not sure what you are doing now, so my apologies if you have done something like this.
Lastly, remember that young tanks do have ups and downs... so until you get to a year or more, then this might just be a blip and you might want to just push right through it. It might take even more than a year for a tank like yours with minimalistic rocks to get really stable with anoxic and oxic zones in the rock and sand to keep the N on the money all of the time.