Reef tank target parameters by tank type
One cheat sheet for Ca, Alk, Mg, pH, nitrate, phosphate, and salinity — and how the targets shift between SPS, mixed, and LPS/soft tanks.
"What should my parameters be?" doesn't have one answer — it depends on what you keep. SPS-dominant tanks want tighter, lower alkalinity and richer Ca/Mg; LPS and soft-coral tanks tolerate a wider, more forgiving band and a little more nutrients. Here's the full reference in one place.
The cheat sheet
| Parameter | SPS-heavy | Mixed reef | LPS / soft |
|---|---|---|---|
| Calcium | 420–440 ppm | 420–450 | 380–450 |
| Alkalinity | 7.5–8.5 dKH | 8.0–9.0 | 8.0–11.0 |
| Magnesium | 1300–1400 ppm | 1280–1400 | 1250–1400 |
| pH | 8.1–8.4 | 7.9–8.4 | 7.8–8.4 |
| Nitrate (NO₃) | 1–5 ppm | 2–10 | 5–20 |
| Phosphate (PO₄) | 0.02–0.06 ppm | 0.03–0.10 | 0.05–0.15 |
| Salinity | 1.025–1.026 | 1.025–1.026 | 1.023–1.026 |
How to read it
- SPS runs tight. Small-polyp stony corals are the most sensitive to alkalinity swings, so SPS keepers aim for a narrow alk band and hold it steady — stability beats chasing a "perfect" number.
- Nutrients aren't zero. Modern reef-keeping wants measurable nitrate and phosphate, not undetectable. Bottomed-out nutrients cause pale, starved corals and dinoflagellate outbreaks. LPS/soft tanks happily run richer.
- Consistency is the real target. A tank held steady at 7.8 dKH is healthier than one bouncing between 8 and 9. Pick a number inside the band for your tank type and keep it stable.
When correcting a low reading, raise alkalinity by no more than ~1.4 dKH per day and split bigger gaps across several days. Sudden alk swings are a leading cause of SPS tissue burn and tank crashes.
Gear this guide uses
Checking your tank against the cheat sheet starts with the tools that read each parameter.
- Cover Ca, Alk, and Mg with a reef test kit for calcium, alkalinity, and magnesium.
- Read salinity accurately with a saltwater refractometer.
- Mix water to those targets with a reef aquarium salt mix.
Some links below are affiliate links — if you buy through them, Moon Dog may earn a small commission at no extra cost to you. We only point to gear we'd actually use.
Sources
Ranges are reference targets, not absolutes. Stability matters more than any single number — confirm with your own test kits and adjust gradually.