Yes, small doses of kelp Iodine can cause detox but vomiting isnt usually one of them. Generally speaking kelp is a poor source of Iodine because the ocean is full of toxins and heavy metals.

Additionally doc in the know report it taking 6-12 MONTHS at 50mg a day to reach sufficiency, 400mcg a day and you will never get there.

Everyone is different hard to say what caused your tummy upset but a bunch pf supps at once can do it, hard to say which or if it was a combination in your case.

I would avoid ester-C if I were you, most people who arent supplementing dont get enough A, D and K to make sure calcium ends up where it needs to go so getting all that extra calcium from ester C over time will generally cause prolems in the form of soft tissue calcification.

It is definitely possible to experience iodine-related detox symptoms when taking Kelp. (I am not sure what "Kelp Iodine" is, though.) Kelp has historically been used as a good source of iodine. Lynne Farrow reports in _The Iodine Crisis_ that archaeological evidence has been found showing that 15,000 years ago a community in South America was using kelp to treat conditions that we now know respond to iodine.

Kelp concentrates Iodine from sea water. Unfortunately, it also concentrates mercury and arsenic. On the Breast Cancer choices web site Lynn Farrow states that "The toxins in
seaweed can now include arsenic, pesticides, radioactive
waste and heavy metals," and says that an iodine-literate practitioner would never prescribe seaweed in any form. http://breastcancerchoices.org/ipractitioners.html

She also says that kelp should be considered contaminated unless one has paid an independent lab to test each batch. You could be experiencing symptoms of toxicity from toxic substances in the kelp. Or you could be having cold or flu symptoms that are completely independent of what you are taking.

800 micrograms of Iodine is a very, very small amount of iodine. Nevertheless, your system does pick up on it. It is essential to do the whole iodine protocol when taking iodine. This includes taking other supplements as well, called "companion nutrients" or "co-supplements." Otherwise, without the whole protocol you could experience health issues instead of benefits. Fortunately, some of the supplements you are taking are on that protocol: magnesium, selenium and Vitamin C. Here is a well-written summary of the protocol:
http://www.stopthethyroidmadness.com/2013/12/29/companion-nutrients-the-key-to-iodine-protocol/

For the protocol you should be taking at least 2,000 mg of Vitamin C. If anything, taking the iodine with no magnesium for the past few days would have been on the negative side as far as the protocol is concerned, not the other way around. Of the other supplements, selenium is one that is definitely needed with iodine, but that is not recommended in doses exceeding 600 mcg -- although I have seen up to 800 mcg recommended for certain cases of Lyme, in a specific Lyme protocol. Most people seem to take 200-400 mcg of selenium. How much selenium is in your multivitamin? Make sure you know your total intake and do some research on the guidelines for selenium.

To take iodine, stop taking the kelp and switch to Lugol's solution or Iodorol or Lugotabs tablets. They contain a mixture of the 2 kinds of iodine that different parts of the body need: Potassium Iodide and iodine.

All the Best --