How much ppm should I add CYM to a in ground spa


Active member
Mar 25, 2014
Arroyo Grande/California
Hi - I just filled my in ground spa with 930 gal of water. I looked at the calculator and all over the forum, but could not find an answer that has a recommendation of how much CYM should be added to a in ground spa when using liquid chlorine. I think 30ppm is correct, but it could be 20ppm or even 50ppm. The directions on the Splash CYM I bought suggested 30ppm, but that could be for a pool.

Thank you.


Mod Squad
LifeTime Supporter
TFP Expert
May 19, 2010
Tucson, AZ
Is the spa usually covered? If so, then you would not need very high CYA levels and I would suggest about 30ppm. If it is not covered and exposed to the sun, then I might lean closer to 50ppm.

You can either add the CYA and then just use bleach, or use PoolMath to calculate how much Dichlor would be needed to get to you desired CYA level and then slowly add that over multiple days to maintain FC as well. Once you put the required CYA in the water, then switch to bleach only.


TFP Expert
Feb 3, 2014
Central Minnesota
This is the thread you're looking for: How do I use Chlorine in my Spa


On a fresh fill use Dichlor until you get to 20-30 ppm CYA. (10 ppm FC = 9 ppm CYA)
Then switch to Clorox Unscented 6% bleach.
Never let FC drop to Zero for any length of time. Keep it between 3-6 ppm normally, min of 1 ppm, and shock to 12 ppm once a week.
Use MPS if needed before hot tub party's and/or once a week to help oxidation. Don't use more than needed, because it's acidic and may lower your TA/pH.
Dichlor, Bleach and MPS is all you need to keep your tub sanitized.
Use PoolMath to calculate exact amounts to add.

And of course, this just popped into my head. (sorry for the randomness)