Should you acid wash a spa filter?
By MySpaFilter Editorial Team · Last reviewed
Usually not. Unicel calls acid washing “perhaps the biggest single factor leading to premature cartridge failure” and says to acid wash only when required, and never without degreasing first[4]. If a drop of acid on clean, rinsed media bubbles, there’s mineral buildup and a mild soak of 1 part muriatic acid to 20 parts water is the published remedy[4].
Unicel’s bubble test
- Degrease the cartridge thoroughly and rinse away all soap[4].
- Put a few drops of acid on a small area of media.
- Bubbling = calcium/mineral buildup → mild acid soak. No bubbling = no acid wash needed[4].
The soak
1 part muriatic acid to 20 parts water until bubbling stops, then rinse[4][1]. Unicel warns that acid-soaking before removing all oils and cleaner causes a permanent flow restriction[4].
Safety
- Wear rubber gloves and safety glasses; don’t add water to acid; never mix chlorine and acid[4].
- Jacuzzi says strong acids like muriatic acid should only be used by professionals and never as a first-step cleaner[10].
If the cartridge is old and scaled, a replacement may be the safer choice — search your part number.
FAQ
What ratio of muriatic acid for a spa filter?
Unicel and Pleatco publish 1 part muriatic acid to 20 parts water, used only after degreasing and rinsing.
Why degrease before acid?
Unicel warns acid-soaking with oils or cleaner still present causes a permanent restriction of flow and premature failure.
Sources
- Pleatco Catalog & Cross Reference Guide — filter care FAQ
- Unicel — Maintenance & FAQ
- Jacuzzi — Hot Tub Filter Cleaning Made Easy
This guide summarizes published manufacturer guidance; always follow your own spa’s owner’s manual. See our disclaimer.