I'm testing CYA with the R-0013 to get it to 30-40 (perhaps a bit higher knowing it will come down).
Perfect. Get to 30 and if you overshoot a little, it's no biggie.
Then, use the calculator,
here to adjust with liquid chlorine. Ex: if CYA is 40ppm, our target Free Chlorine (FC) is 5-7)
I like the app. The forum calculator works too, as does the 'old poolmath page' link towards the bottom of any forum page.
So with a spa, the target level won't swing to UV loss like a pool would. As said above, daily swing will be all over the place depending on use. The poolmath targets are so the sun can burn off 4ppm a day in the peak season.
Personally, I overshoot target range to fall back into it and remain freeeeeeee and clear from min. Look how much wiggle room you have between high target and slam. And look how little there is from low target to minimum.
At 30 CYA, you can start at 9, lose 4 from your soak, and still be golden. If you start at 5, 'in range', you're left with 1 and below min.
For non use times, just ensure you have enough FC to make it to the next test. Say. It's consuming 1ppm a day and you're testing in 2 days. That same 5ppm that wasn't fine for use, is fine for idle time.
*examples used as theory. Enjoy it and see how it behaves.
Chlorine is tested via the K-1515A kit.
Yup.
Enter those values into the Free Chlorine tab in the PoolMath app to determine how much liquid chlorine to add.
Yup. Make sure you have wiggle room before a soak, knowing it will dip. Make sure the residuals didn't wipe you out the next day.
Continue to monitor and test daily, ad infinitum
Yup. You'll get that spidey sense eventually and know it needs XXX when used by you, by 2 people, by nobody, etc. Testing will conform what you know. Eventually you'll be more comfortable and skip some test days when FC loss is steady with no use.
If you use the tub multiple times in a day, test those times like it's a new day.