Salinity 35 ppt (SG 1.026), temperature 24–26 °C, alkalinity 7–11 dKH, calcium 380–450 mg/L, magnesium 1,250–1,350 mg/L, nitrate low but measurable, phosphate around 0.02–0.1 mg/L, pH 7.8–8.5. The table below adds units, testing frequency and how fast it’s safe to change each one.
The cheat sheet
Print this page and keep it near the tank. Each figure links back to a guide with the sources and the detail.
| Parameter | Target | Natural seawater | Unit | Test | Change no faster than |
|---|---|---|---|---|---|
| Salinity | 35 (SG about 1.026) | 34–36 | ppt | Weekly | Slowly, over days |
| Temperature | 24–26 (act above 28) | Varies | °C | Daily glance | Slowly; avoid sudden swings |
| Alkalinity | 7–11 | About 7 | dKH | Weekly; daily when setting a dose | About 1–1.4 dKH a day |
| Calcium | 380–450 | About 420 | mg/L | Every 1–2 weeks | 50 mg/L a day |
| Magnesium | 1,250–1,350 | About 1,280 | mg/L | Every 2–4 weeks | 100 mg/L a day |
| Nitrate | About 2–10 (mixed reef) | Below 0.1 | mg/L NO₃ | Weekly | Gradually, over weeks |
| Phosphate | About 0.02–0.1 | About 0.005 | mg/L PO₄ | Weekly | Gradually, over weeks |
| pH | 7.8–8.5 (8.1–8.3 better) | 8.0–8.3 | – | Same time of day | Follow alkalinity |
Targets from Holmes-Farley, Red Sea, Bulk Reef Supply and Charterhouse Aquatics; daily-change limits from Bulk Reef Supply’s dosing instructions. Testing frequencies are common practice.
Unit conversions
Alkalinity: 1 meq/L = 2.8 dKH = 50 ppm. Phosphorus (P) × 3.07 = phosphate (PO₄). Nitrate-nitrogen (NO₃-N) × 4.43 = nitrate (NO₃). Use the alkalinity converter and the salinity converter for the rest.
How to use it
Steady beats perfect. If your tank sits slightly outside a range but has been steady and your corals look well, don’t rush to change it. If a number moves suddenly, check the test before the tank: see test kit mistakes.
Common questions
What are the most important reef parameters?
Salinity, temperature and alkalinity, because they move fastest and cause the most trouble.
Can I print this?
Yes. Use your browser’s print option; the page prints without the site menus.
Why is the nitrate target a range?
Sources disagree, and the right level depends on your corals. See the nitrate guide.
Sources and limits
Last checked 12 October 2026. Ranges and doses here come from the published sources below and from the chemistry of each additive. They’re starting points for your own tank, not guarantees for any coral.
- Randy Holmes-Farley, Reefkeeping: Reef Aquarium Water Parameters
- Red Sea: Algae Management Program manual
- Bulk Reef Supply: calcium chloride dosing instructions
- Bulk Reef Supply: magnesium supplement mixing guidance
- Charterhouse Aquatics: heatwave survival guide
Keep going
Read the full parameters guide · Free Reef Companion · All calculators