This table below lists the major elements in natural seawater. These elements total 99.5% of all seawater elements. The remainder is considered trace elements. We should spend time managing the major elements before we start playing with trace elements (other than iodine). As testing methods continue to improve, we see many aquarium systems low in many of these major elements. Most of us manage the Big 3: Calcium, Alkalinity, and Magnesium properly; however Potassium, Strontium, Bromide, Fluoride, and Iodine can be just as important. These elements are available from MECoral in 2 oz concentrated bottles. Please visit Mecoral.com.