Glossary
Polyp extension
How far the animal opens its tentacles — the fastest read on whether it is comfortable.
A coral that stays closed is telling you something about flow, light, water or neighbours. We hold an animal for six weeks partly to see whether extension holds through a full cycle rather than on a good day.
Related terms
- Alkalinity (KH)How much carbonate the water carries, and the single number stony corals care most about.
- Sweeper tentacleA long stinging tentacle some corals extend at night to clear their neighbours.