LA Spas HTF-303 Filter Cartridge
LA Spas OEM number • 30 sq ft • 5.375″ OD × 8.5625″ long
HTF-303 is LA Spas's number for this cartridge, not a part you have to buy from LA Spas. The filter itself is a 30 square foot cartridge measuring 5.375 inches across and 8.5625 inches long, and Pleatco, Unicel, and Filbur all build it. If you read HTF-303 off an old cartridge or found it in your manual, any of the numbers below drops into the same housing.
LA Spas also lists FD-51500 against this cartridge. Different numbers on paper, same filter in the box.
Fitment notes
Semi-circular handle top with a 3 inch male pipe thread on the bottom, which is an unusually large fitting and the thing to check first. Pleatco sells it as the replacement for an LA Spas bag filter and Unicel describes its 5CH-203 the same way, as a sock filter substitute. The rating is the weak point of this record: Pleatco's catalog says 30 sq ft, Unicel says 20 for the 5CH-203, and the part number says 35. The 30 recorded here is Pleatco's figure for its own part. The two sheets also disagree on length, Pleatco giving 8-9/16 inches against Unicel's 7.
What to buy instead
Replacements for the LA Spas HTF-303
Each button searches Amazon for one of the numbers this cartridge is sold under. The OEM version is usually the most expensive of the set and the aftermarket versions are the same physical filter, so it is worth checking all of them before you order.
Every number for this filter
| Brand | Part Number | Type |
|---|---|---|
| LA Spas | HTF-303 | The number you searched |
| Pleatco | PLAS35 | Aftermarket equivalent |
| Unicel | 5CH-203 | Aftermarket equivalent |
| Filbur | FC-0303 | Aftermarket equivalent |
| LA Spas | FD-51500 | Other OEM number |
Full specs, the cartridge diagram, and the complete compatibility list live on the PLAS35 cartridge page. You can also see every 5.375″ × 8.5625″ cartridge if you are checking a measurement rather than a part number.
Equipment that uses this cartridge
Looking for a different model? Browse every LA Spas model we cover.
Frequently Asked Questions
What filter replaces the LA Spas HTF-303?
The PLAS35 replaces it directly, and so does every cross-reference for it: 5CH-203, FC-0303. All of them are the same 30 sq ft cartridge at 5.375" outer diameter and 8.5625" long. Buy whichever is cheapest at the time with solid recent reviews. The same cartridge also shows up as LA Spas FD-51500, so those are not different filters either.
Is the LA Spas HTF-303 the same as the PLAS35?
Yes, physically the same filter. LA Spas HTF-303 is an OEM number, meaning it is the code LA Spas put on the cartridge that shipped with the equipment. LA Spas does not manufacture cartridges. Pleatco, Unicel, and Filbur do, and they sell the identical part under their own numbers at a lower price. Match the dimensions against your old cartridge before ordering and you are covered.
Do I have to buy the LA Spas version?
No. Nothing about the housing requires an OEM-branded cartridge, and the warranty on your equipment is not voided by using an aftermarket filter that meets the same spec. The reason to buy OEM is convenience, not performance. The reason not to is price, which is often a meaningful gap for an identical part. What matters is that outer diameter, length, and end-cap style all match.
What size is the LA Spas HTF-303?
5.375 inches in outer diameter, 8.5625 inches long, with 30 square feet of filter media. Both measurements need to land within about an eighth of an inch, and the end caps have to match so the cartridge seats correctly when you close the lid. Measure your old one rather than trusting a number that has worn off the label.
Last verified September 2026