Identifying Calcium Scale
Calcium scale appears as a white, gray, or brownish chalky crust concentrated at the waterline. It feels rough or gritty and doesn't wipe away with a pool brush — it requires chemical dissolution to remove.
Identifying Algae
Algae on pool tile usually appears green, black, or occasionally pink, often with a slimy texture. It typically responds to shock treatment and brushing far more readily than calcium scale.
Why the Distinction Matters
Treating calcium scale like algae won't remove it, while treating algae with harsh acid-based descaling chemistry meant for calcium is unnecessarily aggressive for what a proper algaecide treatment would resolve more effectively.