Dry Acid OK to use in a spa? Yay or nay?

Nigel459

Active member
Mar 9, 2019
27
Ontario
Hi all, I've searched the "Is dry acid ok in spa?" question posed. It seems like the regular advice is avoid dry acid due to the resulting sulphates in the water being harsh on metals and potential for calcium sulphate scale building...

But then I came across an adamant stance in this post that states,

"First of all you will not have damaging accumulation of sulfates if spa water is replaced every few months. Secondly many modern standalone spas heaters are a different design then the copper coils in pool heaters. Many spas use waste heat from the circulation motors to heat the water."

The first part sounds logical: if you don't add much dry acid, and you replace your water regularly, sulphates won't accumulate to damaging levels. As for the second part, I'm pretty sure my Hot Spot SX spa has some sort of copper/metallic heater coil. I am also using a SWCG (Controlomatic--awesome btw).

My fill water TA is high, in the 250 range so I need to bring that down with many rounds of acid additions after a refill...

I'm getting low on MA. I do have a boat load of dry acid, but wanted to get some sort of consensus on this one before using it, thanks!
 
Use your dry acid and drain you spa regularly. It is not a big deal given the circumstances.
 
How does regular draining help, if I dump in all the dry acid right after filling to reduce TA to 60 or so from 250? (Per the method of dropping pH to 7.0 then aerating, repeat etc)


It is the accumulation of sulfates over time that causes damage. A little bit of sulfates is fine. Draining your spa clears out the sulfates and you begin from 0 again.
 
Ok thanks very much. Sounds like you’re saying the difference from spa to pool is the lack of accumulation of chemicals resulting from the evaporation/addition process with a pool.

Since it’s the tfp way, what are the numbers on this? Is there an accepted concentration of sulfates below which is ok? Thanks again!
 
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