How to Cycle a Reef Tank Before Adding Fish

A reef tank cycles the same way freshwater does: bacteria convert ammonia to nitrite, then nitrate. Live rock and sand often seed bacteria, but you still need time and testing before adding fish. Expect several weeks — sometimes longer if rock was dry shipped.

Test ammonia, nitrite, and nitrate every two to three days during the cycle. Both ammonia and nitrite must read zero before any fish. Nitrate may appear and is acceptable in moderation until you export it with water changes.

Avoid adding corals on day one. Let temperature and salinity stay stable first. Log each test in ReefDiary — a photo of the test vial colors next to the logged values helps when you look back months later.