1) Only when coraline algae growth is present.
2) Only when the growth of micro or macroalgae is present.
3) Only when sponges, tube worms, and/or other such sessile invertebrate growth is visible.
4) When a combination of any the above life is present.
5) As soon as it becomes seeded with unseen beneficial microscopic nitrifying bacteria.
Stan & Debbie Hauter Saltwater Aquariums Guides
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