Alk + Calc Balance
Alkalinity and Calcium must stay in balance. Raising Alk without matching Calcium leads to precipitation, dropping both out of solution as calcium carbonate snow. Aim for Alk 8–9 dKH when Calcium is 420–440 ppm.
Mag Supports Both
Magnesium is the stabiliser that prevents Calcium and Alkalinity from spontaneously precipitating. Low Mg (below 1200 ppm) causes Alk and Calc to crash together. Always test Mag when you can't hold Alk or Calc.
pH and Alk Link
pH fluctuates naturally — lower at night (CO₂ builds up) and higher in the day (photosynthesis consumes CO₂). Alkalinity acts as a pH buffer, resisting swings. Low Alk means volatile pH. Open a window near your sump to raise pH naturally.
Nitrate & Phosphate
Both drive nuisance algae and stress SPS corals. The ratio also matters — high NO₃ relative to PO₄ causes pale, bleached tips on Acropora. Maintain a 100:1 NO₃ to PO₄ ratio as a rough guide for SPS systems.
Salinity & Temp
Evaporation raises salinity while raising temperature. In a hot room, both go up together — a dangerous combination that stresses every organism. Use an ATO (auto top-off) with RO/DI water to maintain stable salinity as temperature fluctuates.
Ammonia & pH
Ammonia toxicity is pH-dependent. At high pH (8.3+) a greater proportion exists as toxic free ammonia (NH₃) rather than the safer ammonium ion (NH₄⁺). Even tiny ammonia readings at reef pH can be lethal. Zero tolerance during cycling.