The 9 Most Important Parameters of a Reef Aquarium

Alkalinity, Ammonia, Calcium, Nitrate, Nitrite, pH, Phosphate, Salinity, Temperature

Let’s take a detailed look at each individual parameter, as well as the ideal values for a reef aquarium:

1. Alkalinity

Alkalinity is a complex concept, but as aquarists, we are mainly concerned with estimating the amount of bicarbonate available in the water. Bicarbonate is essential for coral health, as it is one of the key "ingredients" used to build their calcareous skeletons.

Ideal alkalinity for a reef aquarium:
The ideal range is 8-12 dKH. The goal is to maintain a stable level, as fluctuations—even within this range—can stress aquarium inhabitants. If alkalinity is too low, increase it gradually using KH buffer to avoid shocking marine life.

2. Ammonia

Ammonia is a toxic waste product in an aquarium. You want ammonia levels to be as close to zero as possible. It is produced when fish die and decompose or when uneaten food and organic matter break down. A healthy biological filtration system eliminates ammonia. Detectable ammonia levels indicate an incomplete nitrogen cycle or a malfunctioning filter.

Ideal ammonia level:
~ 0 ppm. Any detectable ammonia is harmful to fish and corals.

3. Calcium

Calcium is another essential element for coral health in a saltwater aquarium. Natural coral reefs have calcium levels between 380-420 ppm, with 400 ppm being a good target. Calcium is particularly important for LPS and SPS corals.

Ideal calcium level:
~ 400 ppm

4. Nitrate

In a cycled aquarium, nitrate presence confirms that the biological filter is functioning. While low nitrate levels are preferred, most marine fish and soft corals tolerate levels around 30-40 ppm.

Ideal nitrate level:
~ 0 ppm, though slightly higher levels can be tolerated.

5. Nitrite

Nitrite is an intermediate byproduct in the nitrogen cycle. Beneficial bacteria convert toxic ammonia into nitrite, which is then further processed into less harmful nitrate. Except during the cycling phase, nitrite levels should always be near zero.

Ideal nitrite level:
~ 0 ppm

6. pH

While the absolute pH value is important, stability is even more crucial. Fluctuations in pH can stress marine life.

Ideal pH range:
~ 8.1-8.4

7. Phosphate

In natural reefs, phosphate is present at around 0.13 ppm. In an aquarium, it promotes algae growth, so it should be kept below 0.2 ppm.

Ideal phosphate level:
< 0.2 ppm

8. Salinity

Ocean salinity is ~35 g/L, but in aquariums, it's typically measured as specific gravity. If your zoanthids close up, check salinity.

Ideal salinity (specific gravity):
1.025, which best replicates natural reef conditions.

9. Temperature

Maintaining a consistent temperature is more important than the exact value.

Ideal temperature range:
73-84°F (22-29°C), with 78°F (25.5°C) being optimal.

To keep your aquarium stable, regularly monitor these parameters using specialized test kits.