Caldera Spas Filters
Caldera Spas are built by Watkins (the Hot Spring company) and use their own open-bottom cartridges: a 7″ body in two lengths, or the 8″ 100 sq ft with a lip seal. Older Caldera tubs push the cartridge onto a fitting instead. Measure the length and look at the bottom.
Find your Caldera Spas filter in 10 seconds
All four Caldera cartridges are offered in Darlly (the older slip-fit also in ProAqua), drop-shipped from US stock. If yours matches none of the cards, send a photo through the form below.
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Showing all 5 resultsSorted by price: high to low
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Caldera Spas Filters
Caldera Spas Filter – 100 Sq Ft Open Bottom – Single – Darlly
$144.99 Add to cart -
Caldera Spas Filters
Caldera Spas Filter – 75 Sq Ft Open Bottom – Single – Darlly
$95.99 Add to cart -
Caldera Spas Filters
Caldera Spas Filter – 50 Sq Ft Open Bottom – Single – Darlly
$88.99 Add to cart -
Caldera Spas Filters
Caldera Spas Filter – 50 Sq Ft Slip Fit Bottom – Single – Darlly
$78.99 Add to cart -
Caldera Spas Filters
Caldera Spas Filter – 50 Sq Ft Slip Fit Bottom – Single – ProAqua – High Flow
$74.99 Add to cart
✅ Not Sure It Fits? Verify Before Ordering
Hot tub filter fitment varies by spa brand, model, year, filter size, thread style and top/bottom style.
To confirm the correct replacement, send clear photos of:
- The label or end cap of your current filter
- Your spa serial number sticker
- The filter well with the filter removed (so we can see the fitting)
EZ Hot Tub Parts confirms fitment before you order, so you do not pay return freight on a wrong filter.
Caldera Spas filter buying guide
Open bottom, 7″ across, handle top. 14-3/4″ long = 75 sq ft (Pleatco PCD75N, Unicel C-7375, Filbur FC-3964, Caldera 1019301) — Darlly; 10-3/4″ long = 50 sq ft (Pleatco PCD50N, Unicel C-7350, Filbur FC-3963, Caldera 1019401) — Darlly. Same well, different length.
Open bottom with lip seal, 8″ across. 16-1/2″ long, 100 sq ft (Pleatco PCD100W, Unicel C-8399, Filbur FC-3965, Caldera 1039607) — Darlly. If your old cartridge has a rubber lip on the bottom, this is it.
Slip-fit, 7″ across (older models). 10-3/4″ long, 50 sq ft with a male slip fitting on the bottom (Pleatco PCD50, Unicel C-7451, Filbur FC-3084, Caldera 033016) — ProAqua / Darlly. Same size as the 50 open bottom; the fitting is the difference.
Not sure which filter brand is right for you? Compare Hurricane, OEM Factory Direct, Pleatco, ProAqua, Darlly and Ego3.
Keep your filters working longer: High Pressure Filter Nozzle | Filter Cleaner | Water Care — and every order over $99 ships free, so a spare set plus cleaner usually rides along at no extra cost.
Confirm your Caldera filter: 75 Open Bottom | 50 Open Bottom | 100 Lip Seal | 50 Slip-Fit
Caldera Spas filter questions
Measure the length of the old cartridge. 14-3/4″ = 75 sq ft, 10-3/4″ = 50 sq ft, 16-1/2″ with a rubber lip = 100 sq ft. If the 10-3/4″ cartridge has a smooth fitting on the bottom instead of an open hole, it is the older slip-fit version. Send a photo through the form above if in doubt.
No. Both brands are made by Watkins, but Hot Spring uses its own threaded and Tri-X cartridges while Caldera uses the open-bottom PCD series on this page. See the Hot Spring page for those.
75 sq ft: Caldera 1019301, Pleatco PCD75N, Unicel C-7375, Filbur FC-3964. 50 sq ft: Caldera 1019401, Pleatco PCD50N, Unicel C-7350, Filbur FC-3963. 100 sq ft: Caldera 1039607, Pleatco PCD100W, Unicel C-8399, Filbur FC-3965. 50 slip-fit: Caldera 033016, Pleatco PCD50, Unicel C-7451, Filbur FC-3084.
Every 12 months with a rinse every 2–4 weeks and a monthly soak in filter cleaner. A second cartridge to rotate lets each one dry fully between uses, which is what keeps the pleats open.