Kent Marine Essential Elements replaces biologically important trace minerals necessary to a healthy marine aquarium. These elements are depleted by natural biological processes or removed unintentionally through protein skimming, ozone, and carbon filtration. Designed for fish only and reef systems, Essential Elements is unmatched in its ability to increase vigor and color! Does not contain detrimental heavy metals, phosphates, nitrates, or silicates. Does not promote undesirable algae growth.