Reef + Coral Water Parameters

Prioritize consistent temperature, salinity, alkalinity, and nutrient availability over chasing one exact number. Test trends, make measured changes, and let the aquarium respond.

Target: 1.023–1.026 specific gravity. Consistency matters more than choosing one value within the range.

Evaporation removes freshwater and leaves salt behind, so replace evaporation with freshwater —not saltwater. RO/DI freshwater is an excellent choice for top-off water. Use a properly calibrated refractometer or another reliable instrument.

Temperature: 75–79°F (24–26°C). Avoid large or rapid changes. pH: 8.0–8.4. Daily variation is normal as photosynthesis and respiration change. If pH remains outside the range, investigate alkalinity, gas exchange, carbon dioxide, and overall water chemistry before adding a pH-adjusting product.

In an established reef aquarium, both ammonia and nitrite should be undetectable. Detectable ammonia can point to immature biological filtration, livestock loss, overfeeding, or excess organic waste and should be investigated promptly.

Nitrate and phosphate are necessary nutrients; zero is not always the goal. Excess can contribute to algae and other problems, while aggressively stripping nutrients can also stress a reef.

General targets: nitrate 1–20 ppm; phosphate 0.01–0.10 ppm.

The best level depends on coral type, feeding, filtration, lighting, and the wider system. Interpret test results alongside coral appearance, coloration, and growth.

These parameters work together and become increasingly important as coral growth and consumption increase.

• Alkalinity: 8–11.5 dKH, or 143–205 ppm as CaCO₃. It supports buffering and carbonate chemistry, especially for stony corals. Avoid large, rapid corrections.
• Calcium: 350–450 ppm. It supports corals, coralline algae, clams, and other calcifying organisms. Monitor calcium and alkalinity together.
• Magnesium: 1,250–1,450 ppm. It helps balance calcium and alkalinity and supports biological processes. Check it when calcium or alkalinity becomes unusually difficult to maintain.

Trace elements support metabolism, pigmentation, photosynthesis, tissue health, and skeletal growth, but they are needed in very small quantities.

• Potassium: approximately 380–420 ppm.
• Iodine: approximately 0.06 ppm total iodine in natural seawater; its different chemical forms make testing and supplementation complex.
• Strontium: approximately 8–10 ppm.
• Boron: approximately 4–5 ppm.

Iron, manganese, molybdenum, zinc, cobalt, vanadium, nickel, bromine, fluorine, and other elements may also matter, but routine individual testing is not necessary for most hobbyists.

Filtered natural seawater and quality synthetic saltwater can both support excellent reef aquariums. Natural seawater provides a broad natural balance, but its parameters can vary with source and conditions.

For synthetic saltwater, start with RO/DI freshwater and follow the manufacturer's mixing instructions. Different salts produce different alkalinity, calcium, magnesium, and trace-element levels, so choose one that matches your aquarium reasonably well.

Regular water changes remove accumulated waste and replenish elements. Before a substantial change, reasonably match the replacement water to the aquarium for:

• Temperature
• Salinity
• Alkalinity

For larger changes or sensitive systems, also check calcium and magnesium. Saltwater replaces saltwater removed during a change; freshwater replaces evaporation.

For newer aquariums, check temperature and salinity frequently. Test alkalinity, nitrate, and phosphate about weekly; calcium every 1–2 weeks; and magnesium every 2–4 weeks.

As coral growth and consumption increase, monitor calcium and alkalinity more often. Advanced or high-demand systems may benefit from periodic ICP analysis.

1. 1Test first and confirm unexpected results when possible.
2. 2Dose only when supplementation is needed and you can monitor the parameter.
3. 3Follow the product instructions, make corrections gradually, and retest.

More trace elements are not necessarily better. Avoid adding individual trace supplements solely because they promise faster growth or brighter color. Practical takeaway: Stable parameters, good husbandry, appropriate nutrients, lighting, water movement, and regular maintenance provide the foundation for a successful reef.

If you're unsure about a test result or what your aquarium needs, bring a water sample to Barrier Reef and our team will be happy to help.