Natural seawater sits at 7 dKH (2.5 meq/L). Most reef tanks run 7 to 11 dKH; stability matters more than the exact number. Daily swing should stay under 0.3 dKH.
Open the full calculator| Tank type | Target |
|---|---|
| Natural seawater | 7 dKH |
| SPS dominant | 7-8.5 dKH (low nutrient) |
| Mixed reef | 7.5-8.5 dKH |
| LPS / soft coral | 8-11 dKH |
Raise no more than 1.4 dKH per day, and watch pH: soda ash lifts pH quickly, sodium bicarbonate barely moves it. If alkalinity is high, stop dosing and let coral consumption bring it down, or do water changes with a lower-alkalinity salt mix. Never chase both alkalinity and pH in the same day.