How to Identify a Replacement Pool Filter Cartridge

Short answer

Identify the tank first, then match the element—not just its height or advertised square footage. Record the complete tank model and revision, the existing cartridge’s exact printed numbers, dimensions and end-cap details. Compare those records with the applicable equipment parts list and the candidate manufacturer’s catalog. Confirm whether the offer contains one element or a complete set before paying.

This is an original, research-based identification and purchase guide, not a hands-on test, universal compatibility finder or installation procedure. Sources were retrieved October 23, 2026. The example below demonstrates how to compare evidence; it does not approve a replacement for an unidentified tank. No prices or performance rankings are assumed.

Safety first: start with accessible labels and existing service records. Never open a pressurized filter. Pentair warns that trapped air can cause violent lid separation, serious injury or death. A pressure reading alone is not permission to open the tank. Use an already safely removed element or a qualified service professional working to the exact model’s instructions; this article does not provide isolation, opening, reassembly or restart steps.

Cartridge identification decision diagram

Decision diagram in words:

1. Identify the tank: record the complete model, revision and applicable parts list. Copy existing element markings exactly, without correcting a token to fit a search result.
2. Use the candidate’s measurement convention: keep diameter, length, top and bottom end-cap details separate. Use only an already safely removed element or qualified service help; this is not an opening procedure.
3. Keep evidence source-specific: attach each dimension to its brand and catalog page. The Unicel 26-1/16-inch and Pleatco 26-inch listings below remain distinct; neither establishes a universal tolerance. Preserve model/date conditions.
4. Confirm complete quantity: distinguish a single cartridge from a packaged set and verify the actual SKU, included count and required number of elements.
5. Compare or hold: resolve consequential differences with the manufacturer before ordering. R173476 compatibility remains unconfirmed here; the diagram does not resolve its conflict with R173576. Compare complete costs and written terms only after fit and quantity are established.

This original purchase-planning illustration is not a universal compatibility chart, performance ranking or filter-opening instruction. Never open a pressurized filter. Unknown fit means hold, not approval; the source-specific conditions below still apply.

Not sure whether the element needs replacing at all? Use the clean-or-replace decision guide and before/after service record to separate model-specific cleaning triggers from replacement evidence before choosing a SKU.

1. Separate tank identity from cartridge identity

Write down the tank maker, complete model, serial/date information and applicable manual revision. Separately copy every readable identifier on the old element, including suffixes and punctuation. Keep a photo reference alongside each entry rather than silently correcting a number to match a search result.

A family name is not always enough. Pentair’s official Clean and Clear Plus support page links separate spring-clamp and cast-clamp manuals. Its 2025 guide includes a spring-clamp compatibility note for filters manufactured before August 2025. That note concerns clamp components; it does not establish every cartridge’s compatibility by date.

If you do not yet know whether the job is an element replacement, repair or whole-filter replacement, resolve that diagnosis first. Our sand, cartridge and DE filter comparison addresses complete equipment replacement and its installation scope. A cartridge-shaped element alone does not establish the filter type: cartridge-style DE equipment has different consumable requirements.

2. Measure using the candidate catalog’s convention

For an already safely removed cartridge, Unicel’s 2026 guide, PDF page 3, requests:

• Outside diameter in inches, measured to ±1/32 inch.
• Length including end caps but excluding handles or other extensions, measured to ±1/16 inch. Unicel recommends measuring through the center if possible rather than along the outside edge.
• Top and bottom end-cap configuration; for open ends, inside diameter measured to ±1/32 inch.
• Equipment maker/model, pleat count to ±2 and whether a center core is present.

These are Unicel’s identification measurement instructions, not a universal installation tolerance or permission to force a near-match into place. Record top and bottom separately: an open hole, molded gasket, handle, closed cap or threaded connection should not disappear into a single “diameter” field. Keep extensions and thread details as separate observations and follow the candidate maker’s identification method.

3. Worked example: Clean and Clear Plus 420

This example is deliberately narrow. It illustrates the evidence for a documented model, not a cross-brand recommendation for every filter called “420.” Match the actual equipment and applicable manual before using any part number.

Start with the equipment parts table

The support-linked Pentair 2025 guide, printed page 11 / PDF page 15, lists under item 6:

Part number	Description in the equipment manual
PCC105	Cartridge, single, C&C 420
PCC105-PAK4	Cartridges, set, C&C 420
ULTRA-A6-PAK4	Ultra Cartridges, set, C&C 420

A single-cartridge offer and a set are not interchangeable price comparisons. Check the seller’s actual package count, exact SKU and included components. This table does not establish media-performance equivalence among the listed options.

Keep catalog dimensions attached to their brand

The Unicel C-7471 entry, PDF page 17, lists 7-inch outside diameter, 26-1/16-inch length, 3-inch open top and bottom, and 105-square-foot media. Its Pentair tables on PDF pages 48 and 50 associate the Clean and Clear Plus 420 with R173576 and legacy 178584, respectively, and specify four elements with a model dated after 11/98 condition. Preserve that condition rather than generalizing to all generations.

The Pleatco 2023 PCC105 detail row, PDF page 34, lists 7-inch outside diameter, 26-inch length and 3-inch top/bottom openings. Do not rewrite both catalogs into one universal length or infer a reason for the difference. Record which candidate and source each measurement belongs to; ask the manufacturer to resolve any mismatch affecting the proposed purchase.

Preserve the conflicting identifier

That Pleatco PCC105 detail row contains R173476, while the same catalog’s CCP420 OEM table on PDF page 15 contains R173576. We have not established that either token is a typo, a supersession or an approved alternative to the other. R173476 compatibility remains unconfirmed here; do not order on that cross-reference alone. No shopping link or fit recommendation is provided for the held identifier.

The useful result of the example is a documented question for the manufacturer, not a claim that the conflict has been solved. An older catalog also does not establish today’s stock, price or latest replacement policy.

4. Original cartridge purchase record

Copy the record below for each candidate, or use our one-page printable cartridge identification purchase record. Leave unknowns marked “Unresolved.” The print companion preserves separate tank/element identity, catalog measurement conventions, exact identifiers and unresolved-fit holds. This is a purchase aid—not authorization to open, modify or operate the filter.

Record field	Your evidence or answer
Tank maker, complete model, serial/date and revision	Unresolved
Applicable manual URL, revision and parts-table page	Unresolved
Accessible tank-label photo or service-record reference	Unresolved
Existing element markings, copied exactly	Unresolved
Number and positions of elements, confirmed from applicable records	Unresolved
Outside diameter and units	Unresolved
End-cap-to-end-cap length; catalog convention used	Unresolved
Separate handle, extension and thread observations	Unresolved
Top configuration and opening measurement	Unresolved
Bottom configuration and opening measurement	Unresolved
Core/pleat details if required by candidate maker	Unresolved
Candidate brand and complete SKU	Unresolved
Exact manufacturer cross-reference, page, retrieval date and model/date conditions	Unresolved
Single or set; included count and required complete quantity	Unresolved
Dated exact-offer price, shipping, tax and exclusions	Unresolved
Conflicts, unknowns and written manufacturer confirmation	Unresolved
Seller’s supplied return and warranty terms	Unresolved

Hold the order if the tank identity, applicable parts list, end-cap fit, required quantity or consequential conflict remains unresolved. Written confirmation should identify the actual tank/revision and candidate SKU, not simply say “fits most pools.” A matching area claim or product photograph cannot substitute for that identification.

When to compare—and when to pause

5. Compare complete offers only after identification

Once the candidate is confirmed for the actual equipment, compare the quantity you need, shipping, tax and any excluded service. Do not compare one element’s advertised price with a complete set’s price, or treat an unknown future lifespan as an established cost advantage.

Use our equipment warranty questions to separate supplied parts/labor terms and excluded expenses. Its existing equipment matrix does not establish coverage for these cartridges. Obtain the terms for the actual cartridge SKU, seller and installation/service arrangement.

If the tank or clamp also needs attention, return to the complete-filter replacement card instead of treating a new element as a diagnosis or repair of the pressure vessel. Correct filtration also does not establish swimming safety; sanitation and water chemistry remain separate checks.