Ack! my friend said iodized salt = very bad for what it does to the water ions....his dad and grandpa have owned a LFS for decades and he swears by constant but light salt use...I guess it's one of those everyone has an opinion topics
Unfortunately it's one of those Aquarium myth things. Opinions are choices with similar results, Salt is harmful to freshwater fish, and this can and has been proven over and over and over. Every argument that anyone has for its long term use can easily be refuted with Science and logic. Na and Cl content is low in Freshwater, and even the rift lakes contain the equivalent of less than 1/4 teaspoon od Sodium Chloride per gallon. If you don't have ich you have no need to prevent it, If your fish are healthy and your tank is clean you hav eno worry of fungus, if your bio-filter is in good shape you have no worry of nitrites, and if you have hard water fish (Mollies) and want to help them out Calcium and magnesium are what they would live with in nature. If you have Brackish fish A marine mix is needed not just NaCl. And if you look at what is in a marine slat mix you'll find it is heavy in calcium and magnesium and will also contain some iodide just like you table salt, but in much higher quantities.
The iodide level in table salt is so minute it would have no real effect, Additionally I frequently add marine iodide to my tanks for the shrimp without ill effects on my fish.
Some Kosher and pickling salts contain Prussiate of soda, which is likewise in really small quantities and not a concern.
dave