Hi - Does anyone know if there is a shelf life for chemicals such as iodine, magnesium, calcium, etc.? Some friends have down sized/taken a break and have passed them to me for use but think they might be a couple of years old. I noticed one had a label from "The Aquarium" ....I'm sure that brings back some memories for us east bayers! ;D Any advice or info on this is greatly appreciated. Last thing I want is to cause tank turmoil from supplementing the tank. Thanks and have a nice evening. Doug