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Signs your hot tub filter is bad (and needs replacing)

By MySpaFilter Editorial Team · Last reviewed

Short answer

Replace a cartridge when cleaning no longer restores it: the time between cleanings keeps getting shorter, flow stays low, or the media is torn or the core collapsed[1][6]. Jacuzzi adds persistent cloudiness despite balanced water, limp pleats that don’t spring back, lasting odor after cleaning, cracked end caps, and flow errors right after cleaning[10].

Checklist

SignSource
Shorter cycles between cleaningsUnicel, Pleatco[6][1]
Low flow / high differential pressureUnicel, Pleatco[6][1]
Torn media or collapsed center coreUnicel, Pleatco[6][1]
Limp or flattened pleats; cracked end capsJacuzzi[10]
Cloudy water or odor that persists after cleaning and balancingJacuzzi[10]
FLO / low-flow errors right after cleaningJacuzzi[10]
Discolored or worn mediaHot Spring[8]

Discoloration alone isn’t proof

Pleatco notes that “white does not indicate clean” and media can discolor over time, while faded end caps can come from chlorine and cyanuric acid — though it can also indicate an old cartridge[3].

Why it matters

Hot Spring warns a clogged filter can trip the high-limit thermostat and shut the spa off[9]. CDC advises regular cartridge replacement per the manufacturer as part of controlling germs like Legionella in hot tubs[14]. Ready to replace? Search your part number.

FAQ

Can a filter look dirty but still be fine?

Yes. Pleatco says white does not mean clean and media can discolor naturally; judge by flow and condition after a proper clean.

What does a FLO error have to do with the filter?

Jacuzzi lists FLO/low-flow errors as a filter-related symptom; rinse and inspect the filter first, and call a dealer if it persists with a clean filter.

Sources

  1. Pleatco Catalog & Cross Reference Guide — filter care FAQ
  2. Pleatco FilterWash information sheet
  3. Unicel — Maintenance & FAQ
  4. Unicel — When to Replace a Cartridge Filter (PDF)
  5. Hot Spring Spas — How Do Hot Tub Filters Work?
  6. Hot Spring Hot Spot Collection Owner’s Manual (2026)
  7. Jacuzzi — Hot Tub Filter Cleaning Made Easy
  8. CDC — Controlling Legionella in Hot Tubs

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

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