Water has a strong chemical or musty odor despite normal sanitizer levels.

Water treatment steps:

• Shock the spa: Add a non-chlorine shock or chlorine shock per Marquis water care guidelines to oxidize organics.
• Clean or replace filters: Remove filters, deep-clean with filter cleaner, or replace if more than 1–2 years old.
• Use a plumbing purge: Before the next drain, run a spa plumbing purge product to remove biofilm from lines, then drain and refill.
• Maintain sanitizer: Keep sanitizer within Marquis-recommended ranges and ensure proper pH and alkalinity.