Why We Recommend Adding Corals on Day One

At PNW Custom, we recommend adding corals on day one of your tank setup and here’s why.

Corals Don’t React to Ammonia Like Fish Do

Unlike fish and most invertebrates, corals don’t rely on hemoglobin to transport oxygen in their bodies, which means they aren’t sensitive to ammonia spikes like fish are. Ammonia becomes toxic to fish because it destroys oxygen transport in blood, but corals aren’t affected in the same way. This makes them resilient during the early stages of a tank’s life when water chemistry is still stabilizing.

Corals Bring Beneficial Bacteria & Biological Diversity

Corals bring a lot of life with them. Many corals carry nitrifying and other beneficial bacteria, sponges, algae, and tiny organisms all around them. These organisms begin populating your aquarium from day one, helping kick-start the biological maturation of your system.

Corals (particularly those attached to live rock) effectively seed your tank with biological diversity in a natural and impactful way.

Why Not Start With Fish or Invertebrates?

Fish and many invertebrates are much more sensitive to ammonia and nitrite spikes which are the two key stages of the nitrogen cycle. Those compounds can reach dangerous levels early in a new tank’s life, and without an established bacterial population, fish and sensitive invertebrates can suffer or even die. Cycling with corals first gives those bacteria a chance to grow naturally without harming more vulnerable animals.

So before you add fish or inverts, allow your aquarium to go through a full nitrogen cycle. Once ammonia and nitrite are consistently at zero and nitrate is stable, your tank is ready for fish and invertebrates. This typically takes several weeks.

A Different Approach

This coral-first method is a concept supported by experienced reef keepers and authors. For example, Reef Builders published an article outlining how adding corals at the beginning of the setup can actually help the biological maturation of the aquarium and reduce water quality swings that often happen when cycling the tank with fish first.

Coral First, Fish Later

This approach helps establish a healthier, more stable reef aquarium from the start.

• Add corals on day one: they help seed beneficial bacteria and bring biodiversity into your system.

• Skip fish and sensitive invertebrates until the tank completes its full cycle.

• Wait for ammonia and nitrite to reach zero before adding livestock: this protects your fish and delicate species from harm.