Adding iodine will have no affect on calcium. What exactly was your iodine level that you feel you need to dose it?
Chemistry And The Aquarium: Iodine in Marine Aquaria: Part I — Advanced Aquarist | Aquarist Magazine and Blog
"I would strongly advise people to not try to maintain 0.06 ppm iodine using supplementation and a test kit.
Why you ask? Isn’t that what we do for most other chemicals of interest? Well, if we could easily and accurately determine the concentrations of the different forms of iodine in aquaria, then I would recommend doing just that. However, if you combine the complexities of having multiple iodine species present with the uncertainty of having hobbyists use very complex test kits that may readily yield incorrect or difficult to interpret results, the stage is set for people driving their total iodine to levels far from what they actually intended. I do not know what levels of iodide or iodate become apparently problematic to real aquaria, but the risk of overdosing in this fashion is not insignificant. Both of the ICP studies reported above found some tanks with substantially elevated total iodine levels. I have no way of knowing how those levels got there, but overdosing of a supplement is one likely way."