Rust Issue: Galvanized Coupling in Pool Supply Line

I think I found the problem. First, there was no rust colored “algae” in the spa…zero. ONly the main pool had rust sponts and in the areas where the sweeper cant reach. The spa ONLY recieves water from the filter. The main pool gets refilled from a garden hose. Attached ar

e photos of the supply line showing the rusted “galvanized” coupling I bought from Lowes.