Thanks for the forum/web site

[Barry]

Just a note of appreciation. Been a spa owner for 15 yrs and realized how much I didn't know about water chemistry. Fought issues constantly thinking all that time - "its the nature of the beast".
Spa dealer who tested my water ignored the 1800 ppm Calcium - CSI off the charts - scaling/water line.
Their products also were expensive and the Chlorine Shock increased my CYA - which I never use to test or control. Bleach is an awesome and cheaper source for chlorinating.
Always was perplexed about the TA and PH marriage. Could not independently control them without the other being affected. Borax and Baking Soda definitely cleared this up.
Lastly, invested in a good test kit K-2006, eliminating the subjective test strips. The "pool calculator" is spot on with recommended dosages. Generic instructions for shocking (once a week) didn't cut it - the formula you provided (raise FC level 10X the CC value) much more precise and effective.
Thanks again for this service...I guess an old dog can learn new tricks.
Barry

[chem geek]

I'm glad the advice on this forum has been helpful to you. Don't forget that after a fresh refill of your spa, you need to use Dichlor for about a week and then switch to bleach after that. You want to have some (but not too much) CYA in the water which is why you should use Dichlor first; otherwise, the chlorine will be too strong, will degrade hot tub covers faster, and will dissipate more quickly.

Also, you may not need to shock as often nor see residual Combined Chlorine (CC) a day after a soak if you use enough chlorine daily. One person-hour (that's per person per hour) of soaking (at a high temp near 104F) will need up to 7 ppm FC in 350 gallons. That's 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of MPS non-chlorine shock and these amounts are independent of spa size and are per person per hour of soaking.

Richard

[Barry]

Found that out early (Dichlor) to raise CYA after fresh fill. You mentioned that I wouldn't have to shock as often with regular use of Chlorine. Recommended limit for CC is .5 - I've had it up to 1.0 before shocking - (This is when I used Dichlor exclusively as a chlorinator). Is 1.0 residual CC still a good trigger point to shock? Also if I establish a CYA level of 30ppm and use bleach exclusively as shock and chlorinator, will that CYA level rise over time? If so why and at what rate? (trying to determine how often I should test it.)
Thanks,
Barry

[chem geek]

Barry,

It depends when you are measuring the CC. If you measure it soon after you've been soaking (after you've added more chlorine if that's when you add it), then you will very likely measure CC (sometimes quite a lot) and that's not a problem since it's just introduced from your sweat during soaking. The ammonia (and byproducts of urea) from your sweat combines very quickly (in seconds to a minute) with chlorine to form monochloramine that is measured as Combined Chlorine (CC). This then takes an hour or so to break down from oxidation with more chlorine. So the time to measure your CC level is before your next soak, not after your soak.

If you've been using the 10 ml sample in the FAS-DPD chlorine test where each drop is 0.5 ppm, then it's not uncommon to see some pink for CC where one drop eliminates it. This does not mean you have 0.5 ppm CC as it could be less. If you use the 25 ml sample where each drop is 0.2 ppm, then taking one or two drops to make the CC test clear is typical and means a CC of up to 0.4 ppm. If it's higher than that, or if you just want to, you can certainly shock with bleach.

The reason you saw higher CC levels when using Dichlor was because the higher CYA levels built up from continued use of Dichlor lower the active chlorine concentration so that slows down the breakpont reaction of chlorine with ammonia so CC sticks around longer. Instead of taking an hour or two to get rid of the CC, it can take many hours to a day.

After you switch from Dichlor to bleach, the CYA will not rise at all. If anything, it may slowly drop from chlorine oxidizing CYA (this is slow so in some tubs is not noticeable while in others over months it is measurable). You can measure the CYA again after 2-3 months to see if it drops -- no point measuring it more often than that as it won't change very quickly. If the CYA gets too low, you can just switch back to using Dichlor for a short time to raise it and then switch back to bleach.

Don't forget that when adding any concentrated chemical to the spa you want to do so slowly over a return flow with the pump running. This will ensure good mixing and prevent any settling of chemical to the bottom of the spa.

Richard

[Barry]

Thanks again, Richard.