The reef parameter chart
| Parameter | Target range | Test how often |
|---|---|---|
| Temperature | 76–78 °F (24–26 °C) | Daily (monitor) |
| Salinity | 1.025–1.026 (≈35 ppt) | Weekly |
| pH | 7.8–8.4 | Weekly / monitor |
| Alkalinity (dKH) | 7–11 dKH | 2–3× per week |
| Calcium | 380–450 ppm | Weekly |
| Magnesium | 1250–1350 ppm | Every 1–2 weeks |
| Nitrate (NO₃) | 2–10 ppm | Weekly |
| Phosphate (PO₄) | 0.03–0.10 ppm | Weekly |
Ranges vary a little by coral type — SPS keepers run tighter and lower on nutrients than a soft-coral tank. The golden rule holds for all of them: stability beats perfection. A steady 9 dKH is better than a number that swings between 7 and 11.
What each parameter does
Alkalinity, calcium & magnesium — the "big three"
These build coral skeletons. Alkalinity (carbonate) is the one that moves fastest and matters most day to day. Calcium and magnesium work alongside it — low magnesium makes it hard to keep calcium and alkalinity stable at the same time, so check it when the big three won't settle.
Nitrate & phosphate — the nutrients
A little of both feeds corals and gives them color. Too much drives algae and browns corals out; too little (bottomed out) starves them and can trigger pale, stringy tissue. Aim for low but present. Here's how to bring nitrate down if it's climbing.
Salinity, temperature & pH — the environment
Salinity and temperature swings stress everything in the tank, so keep them boringly consistent. pH naturally drifts up in daylight and down at night; a stable daily rhythm matters more than any single reading.
How to actually keep them stable
- Test on a schedule, not just when something looks off.
- Change one thing at a time and re-test before changing the next.
- Top off evaporation with fresh RO/DI, not saltwater, to hold salinity steady.
- Dose to replace what corals consume (alkalinity first) rather than chasing numbers after they crash.
Watch the trend, not just the number
A single test is a snapshot; reef health is about the trend line. TankMate lets you log every parameter in seconds, charts them over time so you catch drift early, and rolls them into a single Tank Health Score — plus an AI read on what your combined numbers mean for your corals. It's free on Google Play.