What alkalinity actually measures

Alkalinity is the water's capacity to neutralize acid. In a reef tank it represents the dissolved buffering compounds (mostly bicarbonate and carbonate) that corals draw on to build their skeletons. The more alkalinity, the more coral growth potential and the more pH stability you have.

Two units are common. dKH (degrees of carbonate hardness) is the German scale that most reefers use day to day. meq/L (milliequivalents per liter) is the chemistry scale that most ICP labs and some test kits report. Conversion is simple: 1 meq/L ≈ 2.8 dKH. So 8 dKH ≈ 2.86 meq/L.

Target alkalinity range for reef tanks

Most reef keepers target alkalinity between 7.5 and 9.5 dKH (about 2.68 to 3.39 meq/L). SPS-dominant tanks tend to run lower (7.5 to 8.5 dKH) for slow stable growth; LPS and mixed-reef tanks can run higher (8.5 to 9.5 dKH) without issues. Soft-coral tanks tolerate the widest range.

The single number matters less than the stability. A tank cruising at a steady 9.0 dKH for six months will out-grow a tank bouncing between 7.6 and 9.4 every two weeks — even if the average is higher in the second tank. Stability beats peak values.

  • SPS-dominant tanks: 7.5 to 8.5 dKH (2.68 to 3.04 meq/L)
  • Mixed reef: 8.0 to 9.0 dKH (2.86 to 3.21 meq/L)
  • LPS-dominant or soft coral: 8.5 to 9.5 dKH (3.04 to 3.39 meq/L)
  • Avoid daily swings greater than 0.5 dKH — corals retract and stress out

How to test alkalinity accurately

Alkalinity test accuracy varies enormously between methods. The most-recommended tests for reef keepers in 2026:

  • Hanna HI755 Checker — colorimeter that reads alkalinity in ppm CaCO3 (divide by 17.86 for dKH). Most accurate single-test option for most reefers; sub-$60. Reef Trak imports HI755 readings directly with automatic dKH conversion.
  • Salifert Alkalinity Test — titration kit, accurate to ~0.1 dKH if you read the color carefully. Reliable, no batteries, but more user-error than the HI755.
  • Red Sea Foundation B Test — part of the Foundation kit family. Solid accuracy, easy to read.
  • ICP test (Aquaforest, ATI, Fauna Marin, Triton, Reef Moonshiner, Reef Zlements, Tropic Marin) — best when you need cross-check accuracy or are diagnosing a drift problem. Reef Trak imports ICP results from all 7 labs.

Test the same way every time. Same kit, same time of day, same person reading the color. Inconsistency in technique is the most common source of "weird alkalinity readings" reefers report.

Why alkalinity drifts (the common causes)

When alkalinity moves outside the normal range, it almost always traces back to one of these causes. The reef-trak way to diagnose is to overlay the parameter chart with the dosing log, livestock log, and maintenance log so cause and effect are visible side by side.

  • Dosing pump miscalibration. The dose amount drifted because the pump head wore in, or the math was set up incorrectly to begin with. Re-calibrate quarterly.
  • Skipped or undersized water changes. Salt mix contributes some alkalinity; consistent water changes maintain a baseline.
  • New SPS additions. SPS corals consume alkalinity faster than other corals. Adding a colony noticeably accelerates consumption within a week.
  • pH issues bouncing alkalinity. Low pH (especially indoor air with high CO2) drives alkalinity down faster than expected.
  • Bacterial bloom or biofilm shift in the tank. Less common but real; can alter buffering capacity.
  • Bad test kit batch or expired reagent. Always rule out by cross-testing with a second method.

How to raise alkalinity (the safe way)

Slow and steady. The rule of thumb is to raise alkalinity by no more than 1.4 dKH per day; corals can tolerate more, but the swing itself causes stress. Most experienced reef keepers raise no more than 0.5 dKH per day to be safe.

The math: 1 mL of standard two-part alkalinity solution (or Red Sea Foundation B, or kalkwasser, or any standard reef alkalinity dosing product) raises a 100-liter tank by roughly 2.0 dKH. Adjust for your tank volume. Reef Trak's dosing calculator handles the math automatically based on your tank size and the specific product you use.

Common dosing products to raise alkalinity:

  • Two-part B (alkalinity) — BRS, Red Sea Foundation B, ESV B, Tropic Marin Bio-Calcium component, etc.
  • All-for-reef products — Tropic Marin All-For-Reef, Red Sea Reef Energy, Aquaforest Component 1+2+3+ — handle alkalinity as part of a combined dose
  • Kalkwasser (calcium hydroxide) — adds alkalinity and calcium together, drives pH up too
  • Calcium reactor — dissolves calcium carbonate media to release calcium and alkalinity in roughly 1:1 ratio

How to lower alkalinity

Lowering alkalinity is trickier than raising it because there is no inverse dose. The standard methods:

  • Stop dosing temporarily and let coral consumption draw it down. Most effective in tanks with SPS growth.
  • Larger or more frequent water changes with a lower-alkalinity salt mix.
  • In emergencies (alkalinity over 11 dKH), small doses of vinegar can be used carefully — typically not recommended without experience.

If your alkalinity is climbing above target, the first thing to check is whether your dosing pump is delivering more than you think it is. Calibration drift over time is the #1 cause of "creeping alkalinity."

How Reef Trak tracks alkalinity

Reef Trak gives alkalinity the full treatment: log results from any test kit (Hanna HI755 with automatic dKH conversion, Salifert, Red Sea Foundation B, ICP labs), see multi-week trend charts, custom range alerts, and the in-app dosing calculator that handles meq/L to dKH conversion and per-product dose math.

The Stability Trak score also weights alkalinity heavily because reefers care about it the most. A 7-day stable alkalinity gets your tank a higher Stability score; a wide swing drops it.