Unicel 4CH-21 Replacement Filter for Various PTL18P4 | 19 Sq. Ft.

Overview

The Unicel 4CH-21 is a pleated polyester cartridge filter element configured for top-load spa filtration applications, providing 19.0 sq ft of filtration area via a Reemay nonwoven polyester media pack. Dimensional specifications: 4-9/16-inch OD, 2-1/8-inch open top with handle, 9-3/4-inch overall length; bottom end cap is ABS injection-molded in a closed-bottom configuration matched to top-load standpipe seating. Media specification is nominal 15-micron filtration efficiency at standard test conditions, with pleat geometry optimized for the low-flow, high-temperature operating envelope characteristic of residential spa circulation pumps. Rated continuous service temperature: 104°F, with intermittent excursions to 120°F acceptable. End cap bond chemistry is rated for continuous immersion in standard spa water chemistry.

Service interval recommendation: spa applications require accelerated maintenance cycles relative to pool elements. Rinse with fresh water every 2–4 weeks; chemical soak in dilute TSP or commercial enzyme cleaner every 4–6 weeks to displace body oils, lotions, and surfactant accumulation that resists water rinsing alone. Replace at ≤ 3-month intervals for daily-use spas and ≤ 6-month intervals for seasonal use; ΔP replacement trigger is ≥ 5 PSI above clean operating baseline. Chemical compatibility: continuous service rated at ≤ 10 ppm free available chlorine or ≤ 30 ppm total bromine; muriatic acid wash at 1:20 dilution (20 minutes maximum exposure) compatible for calcium scale removal, followed by thorough fresh-water rinse. Enzyme cleaner compatible without restriction. Standard Unicel 90-day manufacturing defect warranty applies through authorized distribution.

What's Included

Your order includes the selected quantity of replacement pool filter cartridges. Each unit is individually inspected for quality before shipping.