[Six-line Wrasse]

Diatoms are typically a post-cycle algae that gradual disappears never to reappear. When you're parameters are reading 0ppm for ammonia, nitrites, and nitrates, add a clean-up crew and you should see your diatom algae problem fade away in a week or so.

Diatom algae blooms are VERY VERY common para- and post- cycle.