How to Choose a Replacement Hot Tub Filter

Direct answer

Start with the filter part number printed on your current cartridge or listed in your spa owner’s manual, and confirm the spa model. Matching dimensions alone does not confirm compatibility. When you must measure, match length, outside diameter, inside opening, and end styles exactly. Approximate size is not enough.

Safety note

Turn the spa off at the control panel, and at the breaker if your manual says to, before removing a filter. Do not run the spa without a filter installed if your manufacturer warns against it. See Can You Run a Hot Tub Without a Filter?.

How TubWise researched this guide

This guide is desk research based on spa manufacturer documentation, filter-maker identification tools, manuals, and related compatibility information. TubWise did not independently lab-test filter cartridges. The focus is selection criteria and fit, not naming a universal winner. Part numbers, dimensions, and availability can change, so confirm current details for your spa before you buy.

Confirm the part number first

Sundance states that exact filter size and part number vary by spa model and year, and that owners should check the owner’s manual for the recommended part number and look at the label on the existing cartridge (Sundance Spas). Some newer Sundance models may use more than one filter housing, so verify the count and location for your model before ordering (Sundance Spas).

Jacuzzi describes its spas as using specific filter cartridges designed for the model’s flow rates and filtration requirements, and directs owners to install cartridges according to the orientation in the owner’s manual (Jacuzzi).

Write down:

1. Spa brand, model, and year if known
2. The OEM or cartridge part number on the end cap or label
3. How many cartridges your spa uses at once

If the label is worn off, use the manual or dealer parts list before guessing from photos online.

Measure when the part number is missing

Matching dimensions alone does not confirm compatibility. Confirm the part number and spa model whenever possible. Use measurements only as a fallback when the label and manual do not give a usable number.

Aftermarket filter makers often organize catalogs by measurement when a part number is unavailable. Pleatco’s Filter Finder, for example, accepts a part number or diameter and length selections (Pleatco). Unicel organizes replacement pleated elements for pool and spa cartridge systems and provides OEM-name lookup paths (Unicel). Treat Pleatco and Unicel as aftermarket identification or cross-reference resources, not as OEM authorities for your spa brand.

Those tools can help you identify candidate replacements. They are not proof that a cartridge will perform like the original equipment filter or satisfy warranty expectations for your spa. Sundance states that look-alike off-brand cartridges can reduce filtration effectiveness, restrict flow, or stress pumps, and recommends genuine Sundance filters or authorized dealers for its spas (Sundance Spas). That is Sundance guidance for Sundance equipment, not a ranking of every aftermarket brand.

When you measure an existing cartridge, record the details the seller or catalog asks for. Common listing fields include:

• Overall length, including the end caps as the listing’s measurement method requires
• Outside diameter across the pleated media
• Inside opening size on each end
• Top-end style: open, closed, handle, or threaded fitting
• Bottom-end style: open, closed, or threaded fitting
• Thread type when a screw-in style is used

Match the replacement to the cartridge you removed on every required field. Do not buy a filter that is only approximately the same size.

Fit and seating

Jacuzzi instructs owners to seat cartridges properly to prevent bypass (Jacuzzi). If water can bypass the cartridge, filtration is reduced because water is not forced through the media. Wrong end style, poor seating, or a cartridge that will not sit as the manual describes are fitment problems to reject before purchase.

Separately, Jacuzzi links clogged filters to reduced jet performance and extra pump load (Jacuzzi). A dirty filter and a wrong-size filter are different issues. On flow-related panel messages, see the scoped guides for Jacuzzi FL1, Sundance FL1, or Gecko FLO if your display matches those pages. A flow code does not prove the filter is the wrong size, and an incorrect filter does not automatically cause FL1, FLO, cloudy water, heater lockout, or pump damage.

Quantity and dual-filter spas

Some spas use one cartridge. Others use two or more in one housing or in staged filtration. Sundance notes dual-stage or multi-housing setups on some models (Sundance Spas). Order the quantity your manual or parts list shows, and replace matched pairs when your manufacturer or dealer instructs you to keep them the same age.

Jacuzzi also describes a rotating spare-filter approach: one set in the spa while another is cleaned and dried (Jacuzzi). That is a maintenance strategy, not a reason to buy a different size.

What not to do when shopping

• Do not buy a filter because the photo looks similar.
• Do not choose by square footage of media alone if the dimensions or end style do not match.
• Do not treat a cross-reference chart as a performance or warranty guarantee.
• Do not install a cartridge that rocks, gaps, or fails to seat the way your manual describes.
• Do not skip confirming the spa model when the seller asks for it.

Safe checks before you order

1. Find the part number on the cartridge label or in the owner’s manual.
2. Note spa brand, model, year, and how many filters the spa uses.
3. If the number is missing, measure length, outside diameter, inside openings, and both end styles.
4. Compare those details to the replacement listing line by line.
5. Inspect the old cartridge for tears or cracked end caps while you have it out; those are replacement cues Jacuzzi lists during filter care (Jacuzzi). Timing guidance lives in When Should You Replace a Hot Tub Filter?.
6. If anything is unclear, ask an authorized dealer with your model and measurements rather than guessing.

When to stop and get help

Stop and contact your dealer or a qualified technician if:

• you cannot confirm the part number or dimensions
• a new cartridge will not seat as the manual describes
• flow problems or error codes continue after a confirmed correct, clean filter
• your spa uses a nonstandard housing your seller cannot identify from the manual

For cleaning method after you have the right cartridge, see How to Clean a Hot Tub Filter. For cloudy water or heating symptoms that involve a dirty filter, see Can a Dirty Filter Make Hot Tub Water Cloudy? and Can a Dirty Filter Stop a Hot Tub From Heating?.