← Glossary · 🐠 Corals
Coralline algae
Coralline algae is the hard, encrusting pink and purple algae that spreads over rock and glass in a mature reef — a welcome sign of stable, healthy water.
Unlike nuisance algae, coralline is desirable: it out-competes pest algae and signals good calcium, alkalinity and magnesium. It needs those minerals stable to spread, so its arrival is a small milestone.