Identifying Calcium Scale
Calcium scale appears as a white, gray, or sometimes brownish chalky crust, typically concentrated right at the waterline where evaporation happens most. It feels rough or gritty to the touch and doesn't wipe away with a simple pool brush — it requires chemical dissolution to remove.
Identifying Algae
Algae on pool tile usually appears green, black, or occasionally pink/mustard-colored, often with a slimy rather than gritty texture. It typically responds to shock treatment and brushing far more readily than calcium scale, since it's a biological growth rather than a mineral deposit.
Why the Distinction Matters
Treating calcium scale like algae (with just extra chlorine and brushing) won't remove it, while treating algae with acid-based descaling chemistry designed for calcium can be an unnecessarily harsh approach for what a proper algaecide treatment would resolve more effectively.