Muriatic acid bad for fiberglass hot tub?


Well-known member
Aug 6, 2018
Hi, I have an Artesian Oahu Elite Hot Tub. I was working to get the pH down and was using muriatic acid which is what I use for my vinyl pool. My local pool store said I shouldn't use that for the hot tub. I forgot what he said could get damaged, I think the steel on the jets? Regardless, I started using the Sodium Bisulfate that came with the start up chemicals. Is it safe to use muriatic acid to lower pH? Or should I stick with Sodium Bisulfate?



Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
Absolutely its safe. Once you put it in the water (moving water) it gets dispersed and diluted. You'd only being using tablespoons of the stuff at a time, right?

Maddie :flower:
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In The Industry
Mar 21, 2020
Cabool, Mo
Just be careful with it. If you spill it on any metal parts it will take the finish off in no time. I used it on a bathtub with bad hard water stains and it took the chrome off of the drain fitting in an instant. It could also damage the skirting depending on what it's made of.
I use muriatic in my spa(s) all the time. Dry acid can also damage surfaces if it gets wet or settles in the spa. Always run jets when adding chemicals.


Well-known member
Oct 4, 2018
Muriatic and other types of acids are routinely used at fairly high strengths for removing algae and algae staining off of fibreglass boat hulls. Muriatic is also great for getting rid of toilet bowl stains as Muriatic acid is often the active ingredient in toilet bowl stain removal products.
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