Product Overview

Keep your Sta-Rite System:3 S7M400 filter operating with the correctly sized inner cartridge. The Pentair 25021-0223S is the 136-square-foot inner replacement module that fits inside the S7M400’s larger outer cartridge. It replaces the inner element when the existing media is damaged, worn, or no longer cleans effectively.

The S7M400 uses two separate cartridges for a combined 400 sq. ft. of filtration area: this 136 sq. ft. inner cartridge and a 264 sq. ft. outer cartridge. This listing is for the inner cartridge only. Check both elements during filter service and replace either one as needed.

Key Features

Genuine Pentair / Sta-Rite replacement cartridge

136 sq. ft. of inner filter media

Designed for the System:3 S7M400 modular media filter

Replaces the smaller cartridge at the center of the filter assembly

Sold individually so the inner element can be replaced without purchasing the outer element

Specifications

Warranty & Compatibility

Compatibility

Confirm “S7M400” on your filter’s model label before ordering. Other System:3 models use different inner cartridges, even when their tanks look similar.

Cleaning & Replacement

Turn off the pump and release all pressure through the filter’s air relief valve before opening the tank. Remove the cartridge according to the filter manual, then inspect the pleats and end caps. Rinse debris from the media as directed by Pentair. Replace the element if the media is torn, the end caps are damaged, or cleaning no longer restores acceptable filter performance.

During reassembly, inspect the outer cartridge, tank seal, and clamp components. Seat both cartridges correctly and follow the filter’s startup procedure, including releasing trapped air. If you need both S7M400 elements, order 25021-0223S for the inner cartridge and 25022-0224S for the outer cartridge.

Customer-Facing Q&A

Q: Is this the inner or outer S7M400 cartridge?
A: This is the 136 sq. ft. inner cartridge.

Q: Does it include the larger cartridge?
A: No. The 264 sq. ft. outer cartridge, part 25022-0224S, is sold separately.

Q: Will it fit an S7M120 or S8M500?
A: No. Pentair assigns those filter models different inner cartridge part numbers.

Q: Do I need to replace both cartridges at the same time?
A: Inspect and clean both. Replace each cartridge based on its condition; this part is available individually.