Best Method for Pool and Spa Sanitation for Chlorine Allergy

[LarryFlorida]

Quick question------

For a 500-600 gal hot tub, I am calculating that ~0.5 oz of ~10.5% liquid chlorine will raise the FC ~1 ppm. Is that close enough to correct?

[PoolDoc]

Do NOT use pool store bleach for this purpose. Industrial bleach can be quite variable in purity and contamination. For this test, use PLAIN 6% brand-name Clorox. Buy it fresh, and store it inside.

600 gallons => ~5000 lbs water
1 ppm => 5000/1,000,000 => 0.005 lb @ 100%
1 gallon of 6% bleach @ 8.6 lbs => 0.51 lbs Cl2 equivalent
So 1 gallon will add 0.51/0.005 ppm, or 102 ppm
1/8 cup is 1/128 gallon, so 1/8 cup will be 102/128 or 0.8 ppm ADDED

BUT . . . . if your original report of 0.5 FC + ~2.0 CC in your tap water was correct, your RESIDUAL (what's left, after reaction) is going to be complicated. HOCl / -OCl reacts with NH4Cl (monochloramine) like this (usually):

NH2Cl + HOCl → NHCl2 + H2O (dichloramine -- somewhat volatile, quite irritating)
and then
NHCl2 + HOCl → NCl3 + H2O (trichloramine aka nitrogen trichloride -- volatile, tear-gas-like in its effect on people)

Now, this is classic breakpoint chlorination chemistry, an old stand-by in pool treatment lore, but one that is rarely applicable. HOWEVER, in your case with your water company supplying MC treated water, it applies

Note that, at each step, you add free chlorine (HOCl), react it with a chloramine, and then get water and an MORE NOXIOUS chloramine! So, if you fill your spa with MC treated tap water with 2 ppm of MC, add 4 ppm of FC, and put your daughter in . . . she's doing to have problems! Do NOT do this.

This is the complexity that caused me to back off on the tub dosing, above.

The BEST way to get a hot tub is to
1. Get the K2006 (I believe I mentioned this before
2. Fill the spa with tap water.
3. Add 1/2 cup of 20 Mule Team borax.
4. Heat.
5. Turn on the aerator / blower / whatever for 10 minutes.
6. Test FC, CC, & pH with the K2006.
7. Add MORE borax if pH is below 8.0
8. Once pH is OK, add 5 ppm of FC per ppm of CC
9. Aerate (and KEEP YOUR DAUGHTER AWAY!)
10. Retest
11. Repeat (adj. pH, then dose with FC, then aerate)
12. Continue till you have an FC > 2.0 and a CC < 0.4.
13. If you get stuck, and aren't making progress, leave it alone for a day and LEAVE IT UNCOVERED IN THE SUN.

But, do NOT put your daughter into the spa till you have a STABLE pH between 7.6 and 8.0, a STABLE FC in the 1.0 - 4.0 range and a STABLE CC level below 0.4 ppm, and do NOT let her stand around the spa, while you are aerating, till the MC / DC / TriC is gone!

(Get a K2006!)