Experience luxurious water with the FROG® Serene® In-Line System. Our FROG systems give you continual Fresh Mineral Water®, so your spa water is clean, clear, and perfectly sanitized. There’s never any worry about measuring chemicals. Simply replace your cartridge when it’s empty for a spa experience that’s like none other. Enjoy the ease and convenience of the unmatched FROG® Serene® In-Line System from Tredway Pools Plus.