salt water chlorine generator question

[cedar tub]

Hello All,
I've been using Nature 2 carts and an electronic copper ionizer in an all cedar tub since Oct.  My water quality has been really nice.  My only problem has been low pH from the tannic acid that leaches from the wood.  That's a temporary problem and an injection of air takes care of it.  I've been using dichlor instead of MPS after I was told MPS is bad for wood tubs.  I follow the N2 recipe and generally 2-tsp per person after use does the job.  Now, since I use dichlor, I have to keep an eye on cya.  There are chlorine generators called the Technichlor and the Colorchlor that use components from my local grocery store.  There is also the spa-pilot brand which uses packets bought from them.  The benefit I see to using Technichlor or Colorchlor is there is no stabilizer added.  Spa-pilot packets have stabilizer.  Once I get a base of stabilizer built up from my dichlor, I could use a Technichlor set for a smaller tub so that the chlorine production stays low...yes, no?

[Vanguard]

Do you keep your tub covered?  If you keep it covered, you don't need to worry about CYA.  CYA is used in swimming pools to keep the effects of the sun from zapping out the chlorine.  But, most pools aren't covered.  Indoor pools don't have to worry about CYA because they are not in the sun.

[cedar tub]

It's always covered.  The problem is the stabilizer is in the dichlor.  Every spa care guide I've read talks about CYA.  Once it gets to a certain level, it takes more chlorine to do the job...or something like that.  I'll be changing the water probably in Feb, so it won't matter.  I think I'll skip the chlorine generator for now.

[chem geek]

Cyanuric Acid (CYA) doesn't just protect chlorine from breakdown by UV in sunlight.  It also binds to chlorine significantly lowering the active chlorine (hypochlorous acid) concentration by orders of magnitude.  If you put in a saltwater chlorine generator (with salt in the water, of course) and didn't have any CYA in the water, your water would be WAY over-chlorinated and would wear on the spa cover and other components much too quickly.  It would be similar to using bleach in the water without first using Dichlor.  If you initially shock with Dichlor or use it for about a week or so, then you'll have some CYA to moderate the chlorine strength from a saltwater chlorine generator.  For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases CYA by 9 ppm.

The fact that CYA isn't used in most indoor pools doesn't mean it's the right thing to do.  Virtually all incidents of respiratory problems and triggered asthma are in indoor pools and the reason may not just be poor air circulation and lack of sunlight.  Without CYA in the water, the production of the most irritating of chloramines, nitrogen trichloride, is orders of magnitude greater -- a factor of 10 or more.  My wife experiences this difference every winter season when she swims in an indoor pool at 2 ppm Free Chlorine (FC) with no CYA where her swimsuits wear out (elasticity gets shot) in just one season, her skin is flaky and hair gets frizzy whereas in our own outdoor pool with 3 ppm FC and 30 ppm CYA during the summer the swimsuits have lasted for years and the effects on skin and hair are minimal.

An FC/CYA ratio of 0.1 (i.e. FC that is 10% of the CYA level) is roughly equivalent to an FC of 0.1 ppm with no CYA at pool temperature and possibly 0.5 ppm FC with no CYA at 104F spa temperatures.

The relationship of chlorine and CYA has been known since at least 1974 as described in this technical paper.  The industry, especially stabilized chlorine manufacturers, only talk about CYA being needed to protect chlorine from sunlight because they don't want you to know that the main reason for getting green algae in pools when the chemical levels "seem right" is from continued use of Trichlor due to the buildup of CYA that reduces chlorine effectiveness unless the FC is proportionately raised.  Though they do offer "algae-free guaranteed" programs when you use a weekly algaecide, they don't tell you that the reason it's needed is because for every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm.  In my own pool, I now only use chlorinating liquid, have stable pH, and never get algae in spite of my pool's phosphate level being between 2000-3000 ppb.

If you don't want to worry about the buildup of CYA when using Dichlor, then you can follow Nitro's description of using Dichlor for a short time and then switch to using bleach as described here.  Be sure and watch your pH and adjust your TA down as needed and/or use Borates.

Richard

[cedar tub]

Thanks Richard,
Since this tub is all cedar, I have to be very careful with my chemicals.  My intention with the salt water chlorine generator was to use it after my CYA reached the range of around 30.  I was thinking the Technichlor could be a solution since it uses common products from my local market and there would be no additional stabilizer added.  I assume the addition of unscented 6% chlorox would be the same as dichlor if I add the same concentration.  Since my method of dosing dichlor after each use has been effective with the N2, I'll stick to that but will use chlorox after my CYA hits 30.