Kent Zoe is a superior vitamin complex for Marine Fish, Invertebrates, and desirable algae. Zoe does not contain phosphates as most competing vitamin supplements do, and will not cause unsightly algae growth. It contains aquaculture grade vitamins, meaning that they are still active after one year in your aquarium. It is unique because it also contains natural minerals from spirulina and kelp sources. Competing products are preserved with glycerin, which is an alcohol and requires 50-percent concentration to preserve. Zoe is properly preserved, using less than 1/2-percent preservatives, yet has a 4 year shelf life with no refrigeration. Just smell the difference.