I think it helps the shrimp molt without incident. I do add it. I do 1 drop per 10 gallons per week after WCs. But, I don't really measure it that exactly. Sometimes it's more like 4-5 drops per gallon, and I have not seen any ill effects. For what it's worth, when I stopped dosing iodine in my invert tank for about 3 months, I lost all my pond snails and ramshorn snails. That was really the only change besides adding some new plants and Eco Complete. No idea which was the real culprit. IMHO, it's better to be safe than sorry, and it's not harmful to add iodine. For a freshwater tank, the small bottles of Kent Marine Iodine will last forever and is a pretty small investment for a possibly large reward.