← Glossary · 💧 Water & chemistry
pH
pH measures how acidic or basic the water is; a reef runs slightly basic, around 8.1–8.4, and stability matters more than chasing an exact figure.
Reef pH naturally dips at night and rises by day. Don't fix a "wrong" pH with additives — a steady value your corals have settled into beats a perfect but unstable one; look at alkalinity, which buffers pH, if it's genuinely swinging.