When to Replace a Hot Tub Filter

The short version: if a cartridge comes out of a proper chemical soak looking clean and still produces weak jets or cloudy water, it is finished. Media that has lost its structure cannot be restored, and every further cleaning attempt is time spent on a part that has already failed.

Six signs it is done

1. The pleats no longer spring back. Squeeze a section and let go. Healthy media returns to shape. Fatigued media stays compressed, and compressed pleats hold debris no rinse will reach.
2. The end caps are deformed or cracked. This is the most consequential failure and the least obvious, because the cartridge still fits. A cap that no longer seals lets water bypass the media completely.
3. The media is torn, frayed or shedding. Usually from a comb used too hard, from pressure washing, or from a bleach soak. Any tear is a bypass.
4. A proper soak no longer restores flow. If the jets are weak before the clean and weak after it, the restriction is in the media structure rather than in the loading.
5. Discoloration that does not shift. A permanent gray or brown stain after a full soak means the media has absorbed contaminants into the fiber rather than holding them on the surface.
6. You are cleaning it constantly. A cartridge needing attention every few days used to need it monthly. That change is the filter telling you its usable area has collapsed.

How long should a cartridge last?

As a planning figure, roughly twelve months on a rinse-weekly, soak-monthly routine with normal household use. That is a planning number rather than a rule, and three things move it:

What running a dead filter actually costs

More than the cartridge. A filter that has stopped filtering means suspended solids stay in suspension, which means you shock more, use more sanitizer, and change the water sooner. It also means less of your volume meets the sanitizer per cycle, which works directly against holding the residual the CDC’s hot tub guidance depends on.^[source]

There is also a pump cost. A badly restricted cartridge makes the pump work against resistance it was not designed for, and in the worst cases that is a heater or pump problem rather than a filter problem.

Before you replace it, rule out the cheaper answers

• Has it had a real chemical soak, not just a rinse? If not, do that first — see how to clean a hot tub filter.
• Is the problem oil or scale? An oil-loaded cartridge soaked in vinegar comes out looking exactly as clogged as it went in.
• Is it seated properly? A cartridge that is not fully seated behaves like a failed one.
• Is the water problem actually the filter? Cloudy water has four common causes and only one of them is filtration. Work through why your hot tub water is cloudy before spending money.

When you do replace it

Buy two. The rotation is what stops the replacement dying as early as its predecessor did, and two aftermarket cartridges frequently cost less than one premium one. Use the filter finder to confirm the part number from the cartridge you are removing, and the cartridge roundup to decide which of the cross-referenced equivalents to order.

And note the date somewhere. A cartridge with a known fit date is much easier to judge than one that has been in there for an unknown length of time, and it turns replacement from a guess into a decision.