budster said:
I'm still with the "chloramines" theory, and I'd suggest some draindown to remove some TDS, and then use a stronger shock, like a dichlor or even a cal-hypo. Other's thoughts? :?:
Jeff had tried shocking to high FC levels before with no discernible effect.
As waterbear said, it's the resulting FC that matters -- the type of chlorine that is used is not relevant except that it adds extra things. With bleach or chlorinating liquid, you do have to add more by weight, but by cost it's actually less expensive than other sources after accounting for the cost of extra chemicals needed to balance the pH (see
this post). The following are useful chemical facts that you should be telling all of your dealers to whom you sell:
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.
Every source of chlorine will convert to chloride as it gets used up so for every 10 ppm FC you will increase salt by 6 ppm. With most hypochlorite sources of chlorine (except Cal-Hypo), these also increase salt by 6 ppm upon addition so have a net increase of salt after usage of 12 ppm.
Obviously, water replacement would remove what is registering as persistent Combined Chlorine (CC), but we're trying to avoid that and find something that might reduce it directly. We've seen this problem at least once before where shocking doesn't do any good at getting rid of the CC. Note that Jeff was able to get rid of the CC in one bucket test where he added more CYA, some FC and ammonia, but didn't do a smell test afterwards. So we're going to try again with what he did with that bucket test, but do the experiment on the spa.
Richard