Why Your Alkalinity Keeps Swinging (And Why SPS Hates It)

Stability matters more than the number

A reef tank holding steady at 7.5 dKH will almost always outperform one swinging between 7 and 10. SPS corals evolved in an environment where alkalinity barely moves day to day — rapid swings stress their calcification process even when the average looks fine on paper.

The usual suspects

• Manual dosing inconsistency. Skipping a day, then "catching up" with a double dose, creates exactly the sawtooth pattern that stresses coral.
• Growing biomass. As SPS frags grow in, alkalinity demand increases — a dose that was stable three months ago may now be too low.
• Evaporation rate shifts from seasonal AC/heating changes, altering kalkwasser drip concentration more than people expect.
• Test kit error. Cheap titration kits have real variance between testers — even between two tests by the same person, minutes apart.

How to actually fix it

Switch to a daily 2-part dose split into smaller, more frequent doses rather than one large daily dose — a doser running 3–4x per day smooths out the curve dramatically compared to once-daily manual dosing.

Track alkalinity for 2 weeks before changing your dose. A single bad reading is noise; a trend across multiple days is signal. ReefMind's trend-based dosing calculator looks at your actual consumption rate over time and tells you the dose to hit a stable target — not a generic recipe.