A happy pool is a clean pool. Remove dirt and debris from your water by keeping your cartridge filter working its best with the Unicel UHD-SR138 hot tub spa filter cartridge replacement. This replacement spa filter cartridge measures 8.68 inches in diameter and 34.5 inches tall. This replacement filter cartridge is Unicel part number UHD-SR137. Use this replacement pool filter cartridge to replace the Sta-Rite T-135TX cartridge in Posi-flow filters. This spa replacement part features an open-top end cap with an open bottom end cap with 12 concentric slots. Make sure you can match these up to your spa's cartridge filter before purchase. Made for efficient and effective cleaning, this pool and spa filter cartridge features fine filter media. The filter cartridge sports 195 pleats and can cover up to 135 square feet of pool water.