How to install a hot tub filter cartridge

Last reviewed October 27, 2026

Turn the spa off, put the new cartridge in the same orientation as the one you removed, and do not overtighten the retainer. Hot Spring’s manual says to cut power before you remove filters, not to use the spa with the cartridge removed, and not to overtighten the filter retainer^[9]. Jacuzzi says the same about power and about running with no filter, because debris then goes to the pump and heater, and it says to keep a second cartridge so the spa is never filter-less while one soaks^[10].

Before you open the well

Installation starts with the right part, not with the lid. If you are not sure the new cartridge matches, stop and use the part-number search or the size guide. A cartridge that is close in length and wrong on the bottom will sit in the housing and not seal. Which ends the catalogs care about is covered in open-end vs threaded hot tub filters.

Then make the spa safe to open. Hot Spring’s Hot Spot collection manual and Jacuzzi’s filter instructions both say to turn the power off before you remove the filter^[9][10]. Jacuzzi’s reason is specific: it stops the pump from starting while your hands are in the well, and it avoids pulling air into the plumbing. Sundance’s air-lock procedure has you take the filter out only with the power off, purge the air, and put the filter back before you restore power^[12].

The steps the manuals share

1. Power off at the spa’s disconnect or the breaker the manual names, not only by setting the jets to zero^[9][10].
2. Lift the old cartridge the way that spa is built. Handle-top cartridges lift by the handle. Open-end cartridges slide off a standpipe. Unicel’s general instruction is to remove the cartridge following the spa maker’s instructions^[4].
3. Look at which end was up. The spec table’s “top” is the end that faced you: a handle, an open hole of a stated size, or a closed cap. Put the new cartridge back the same way. On a threaded bottom, the thread goes onto the fitting you just unscrewed the old one from. On a male-slip bottom, the stub goes into the receiver. Do not flip an open-end cartridge end for end if the two holes are different sizes. Sundance C-8326, for example, has a 1-1/2" male slip on one end and a 2-1/2" opening on the other^[5].
4. Seat it and snug the retainer. Hot Spring says not to overtighten the filter retainer^[9]. Cracking an end cap by cranking the retainer is a failed install, not a tighter seal.
5. Restore power only after the cartridge is in. Sundance’s purge steps end with the filter reinstalled before power returns^[12]. Hot Spring says not to use the spa with the cartridge removed^[9]. Jacuzzi advises against running with no filter installed^[10].
6. Watch the first cycle. A flow error right after a filter change is often air or water level, not a bad new cartridge. The code-by-code version is hot tub flow errors and your filter.

If the housing holds more than one

Some spas do not hold a single cartridge. The Leisure Time listing for Hot Spring OEM 71825 says many of those models take three of the 6" cartridges^[38]. Unicel says Master Spas Eco-Pur systems from 2006 on require two C-8341 cartridges, plus the separate inner element^[5]. Sundance’s 680 and 780 manuals describe a pleated outer filter and a disposable MicroClean insert, and they give those two pieces different replacement intervals^[11][12]. Count the pieces you removed. Install the same count. A guide to those systems is spas that use more than one filter.

The insert is not cleaned like the outer cartridge. Sundance says never to use filter cleaners on the inner inserts, and its 680 manual specifies a low-pressure rinse and no chemicals on the insert, while the outer pleated filter is the one that gets a stronger hose rinse^[11]. Putting the insert through the degreaser soak Unicel describes for a pleated cartridge is the wrong procedure for that piece.

The second cartridge is a spare, not a stack

Unicel, Pleatco and Jacuzzi all tell owners to alternate two sets so one can be cleaned and dried while the other is in the spa^[4][1][10]. Jacuzzi says a filter can go back in damp, and that letting a set dry completely is what extends its life. That second set lives on a shelf. It is not a second cartridge shoved into a housing designed for one, unless the spa’s own list says the housing holds two or three. Buying a two-pack of an Intex S1 cartridge is the same idea: the pack is spares of one type, and Intex’s lists still require you to pick S1 or S2. See Intex and Bestway filters.

What not to do in the same visit

• Do not run the pump “just to test” with the well empty. That is the thing Jacuzzi and Hot Spring say not to do^[10][9].
• Do not acid-wash a new cartridge. Acid is Unicel’s last step for mineral scale on a cartridge you are trying to save, and only after a degrease. Unicel calls acid washing a leading cause of early cartridge failure^[4]. A new cartridge does not need it. The full caution is in should you acid wash a spa filter?
• Do not put any cartridge in a dishwasher. Jacuzzi says dishwashers and washing machines can warp end caps and do not clean between the pleats^[10].
• Do not ignore a retainer that will not close. If the lid or the retainer will not seat, the cartridge is too long, the handle is on the wrong end, or a stand pipe Unicel told you to remove is still in the well. Master Spas notes that stand pipe on specific part numbers^[5]. See Master Spas Eco-Pur filters.

After it is in

Rinse residue matters on a cartridge you just cleaned, more than on one fresh from the package. Jacuzzi warns that cleaner left in the media foams once the jets run^[10]. If you installed a cartridge that has been soaking, rinse it until the water runs clear, using the top-down hose method Unicel and Pleatco describe^[4][1]. Then balance the water. A new filter does not set pH. Hot Spring’s published ranges for its own spas are a separate job, covered in how to balance pH and alkalinity.

Replace, rather than reinstall, when the media is torn, the core is collapsed, or cleaning no longer restores flow^[6][1]. Those signs are listed in signs your hot tub filter is bad. Intervals by brand are in how often to replace a hot tub filter.

Questions

Sources

1. Pleatco Catalog & Cross Reference Guide: filter care FAQ
4. Unicel: Maintenance & FAQ
5. Unicel 2026 Replacement Guide
6. Unicel: When to Replace a Cartridge Filter (PDF)
9. Hot Spring Hot Spot Collection Owner’s Manual (2026)
10. Jacuzzi: Hot Tub Filter Cleaning Made Easy
11. Sundance Spas 680 Series Owner’s Manual (2024)
12. Sundance Spas 780 Series Owner’s Manual (2024)
38. Leisure Time Inc.: Hot Spring Highlife 71825 filter cartridge

This guide summarizes published manufacturer and public-health guidance; always follow your own spa’s owner’s manual. See our disclaimer.