My CYA is 151. Around 110 I started using 6% bleach (ya, I now know too late) but the CYA has continued to climb to 151 today as measured by dealer's ALEX system. The person doing the test at the dealer suggested liquid chlorine or bleach burns off faster than granules. I don't recall reading that here or elsewhere so can anyone confirm if this is true?
At 151 CYA I guess it's time to do at least a partial water change. If I stopped using Dichlor and only used bleach will CYA ever drop or will the level remain constant?
It is complete and total B.S. that chlorinating liquid or bleach "burns off faster than granules". Once ANY source of chlorine dissolves in the water it produces EXACTLY the same type of chlorine -- the only difference is what ELSE the type of chlorine adds. The following are chemical facts that are independent of concentration of product or of spa (or pool) size.
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 Cal-Hypo by at least 7 ppm.
For ANY type of chlorine, for every 10 ppm FC the chorine when used/consumed will become 8 ppm salt. When using most hypochlorite sources of chlorine (e.g. chlorinating liquid, bleach, lithium hypochlorite), there is an additional 8 ppm salt added upon addition.
What the dealer may be referring to is if you were to use ONLY bleach with no CYA in the water at all. In that case, the active chlorine level is far too strong and it will outgas faster and react faster so get used up more quickly. However, that's not the proper way to use bleach. One should initially add or build up CYA to the water which one can do either by adding pure CYA initially or more easily can just use Dichlor for a while until the CYA builds up. Then switch to using bleach. About once a month, use Dichlor for a day to build CYA back up since it slowly gets oxidized by chlorine at a rate of roughly 5 ppm per month in spas.
So if you stopped using Dichlor your CYA will SLOWLY drop, but for practical purposes it won't drop fast enough. As for when CYA becomes a problem, technically you can just raise your FC target proportionally for the same active chlorine level. 3 ppm FC with 30 ppm CYA has the same active chlorine as 10 ppm FC with 100 ppm CYA or 20 ppm FC with 200 ppm CYA. However, most people don't want to start their soak with a high FC level -- not because the chlorine is too active (because it's not), but because they want to avoid the smell of chloramines that will result from the chlorine reacting with ammonia and other chemicals (such as urea) in your sweat and urine. Usually people add a large amount of chlorine AFTER their soak in a quantity sufficient to oxidize their bather waste and still have a 1-2 ppm FC residual 24 hours later for their next soak (if they soak every day).
As for whether 151 ppm CYA is too high, it's not so bad as to when rates of hot tub itch/rash/lung seemed to be more prevalent which was at around 200 ppm or higher (though there was one incident between 100 and 200 ppm CYA) and it's also not as high as when a water change is typically needed due to the water getting more dull which is roughly at 250 ppm CYA (i.e. after 272 ppm FC has been cumulatively added from Dichlor). So up to you as to whether you want to do, say, a half drain/refill to get to around 75 ppm CYA which is certainly reasonable (the 30-40 ppm CYA target is to have a somewhat higher active chlorine level for reasonably fast oxidation of bather waste while not being too high).
