Which filter does my Caldera hot tub take? Lookup by model and year

Reviewed October 25, 2026

The dealer fitment table lists seven Caldera cartridge numbers across these series, and several models switch cartridge partway through their run: for example the Utopia Geneva, Niagara and Tahitian take the 7" × 14-3/4" 73531 through 2004 and the 8" × 16-1/2" 73722 from 2005. Most current Paradise models (Salina, Reunion, Seychelles, Makena) are listed for 73531, and Kauai and Martinique for the shorter 73532. Find your model below and confirm against the number on the old cartridge, because the dealer table flags several model-years as needing a serial-number check.

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The cartridges, with equivalents

Equivalents and sizes are from the Unicel 2026 Replacement Guide unless the table says otherwise. A part number in brackets is another factory number for the same cartridge in Unicel’s cross-reference.

Find your model

Rows show the factory part number, then the model years it is listed for. Where two part numbers are joined by “or”, the dealer table lists both for those years. Years are from one dealer’s table and are the least certain part of this page; the part number on your old cartridge wins.

Utopia

Paradise

Highland

Vacanza

Aquatic Melodies

C-Series

Model-years the dealer flags for a double-check

• Paradise Makena 2024: confirm the spa serial number before ordering. The table lists 73532 for 2024 only and 73531 for the other Makena years.
• Paradise Hawaiian HAA 2004: the dealer asks for the spa serial number before ordering.
• Aventine 2019: the dealer asks for the spa serial number to confirm the filter.
• Utopia Cantabria 2014: confirm the production quarter. Q1–Q2 production uses 74817 and Q3–Q4 uses 73722.

Where the dealer tables differ

The model-year table here comes from a single dealer, and other listings do not match it exactly. That dealer’s own product page for the 73531 gives Tahitian as 2002–2005 and Elation as 2003–2008, while its fitment guide gives Paradise Tahitian TAA as 2000–2005 and Elation as 2003–2004 for the 73531 (it moves Elation 2005–2008 to the 73722). A second retailer lists the 73531 for the Paradise series as 2003 to current, and sells the 8" × 16-1/2", 100 sq ft cartridge for the Utopia Geneva from 2005 on, which agrees with the table below. Treat first and last years as approximate.

How to confirm yours

1. Read the part number printed on the old cartridge. The dealer itself says that even within one Caldera model line the filter can change by year, and that the part number is the most reliable method.
2. Measure the diameter and length if it is unreadable: 7" × 14-3/4" is the 73531 family, 7" × 10-3/4" the 73532, and 8" × 16-1/2" the 73722 or 74817. Our filter-size guide shows how.
3. For the model-years flagged above, have the spa serial number ready and ask a Caldera dealer.

Why one cartridge size can carry two different square-foot ratings: our explainer with Unicel’s pleat-count table.

Sources

1. Leisure Time Inc.: Hot Tub Filter Fitment Guide (Caldera tables; fetched 2026-10-25)
2. Unicel 2026 Replacement Guide: Caldera Spas cross-reference (printed p. 26) and Hot Springs cross-reference (p. 35)
3. Leisure Time Inc.: Caldera 73531 product page (specifications, model-year list, filter FAQ)
4. SpaStore.com: Caldera 73531 / PCD75N listing (model years; related 8" × 16-1/2" Utopia filter)

This page summarizes published catalogs and dealer fitment tables; always follow your own spa’s owner’s manual. See our disclaimer and methodology.