Bleach Method - Ph/ta Imbalance

[denvertub]

I've been using the bleach method successfully since buying my Hotsprings Grandee five years ago. Just had it tuned up at which time the tech cleaned the lines but I can't remember the name of the product used and he also increased the ozone bubble flow. He emptied and filled the tub but I told him I would take care of the chemicals. I did my usual set up with the same amounts of calcium and borates (mule team) which has worked on every tub change but now I can't get the ph and ta in line. When I attempted to lower the ph and ta after the adding borates and ca, the ta comes down more rapidly than ph so I'm stuck at ph 8.2 and ta 40 ppm. I used the pool calculator to arrive at CA and borates levels. Calcium is at 150 ppm and I added 28 oz of borates (although it was an older box and clumpy in the measuring cup). I've been aerating as usual during the balance process. Any help would be greatly appreciated.

Thanks

[chem geek]

28 fluid ounces volume of boric acid to add 50 ppm borates would be for a spa of around 680 gallons which sounds high. The Grandee is 500 gallons, isn't it? That would be 21 fluid ounces volume of boric acid. So you probably added too much, but not horribly much.If your pH isn't coming down with acid, I suspect your pH reading is wrong and that may have a high chlorine level that is bleaching out part of the phenol red test. See the following from Taylor Technologies:

FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purple color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.

I also presume you started off using Dichlor and not bleach since adding bleach with no CYA in the water is far too harsh since the active chlorine level will be too high.

[denvertub]

Thanks for your reply Richard!

Interesting... When I plug 500 gallons into the pool calculator I arrive at 28 oz borax by volume to arrive at 50 ppm borates. That's what I've been using for the past 5 years. How did you come up with your calculation? Assuming you are correct, should I replace some water to lower borates? ... and how might the higher borate level effect the other measurements?

Anyhow, the problem that I'm having is that TA drops too much when I add enough acid to bring me to my target ph. I've been using a properly calibrated Milwaukee digital ph meter that I happen to have for my marine aquarium. I just used the Taylor color test kit as well and they're both close enough such that I think I have a proper ph reading. After a few tries raising the water to about 100 ppm TA and lowering with acid while aerating, I just tested again and I'm at about 7.7 ph and about 45 ppm TA. Tub is at 102 degrees. Based upon Nitro's article, I should be at 7.6 ph and 80 ppm TA with CH at 150. Thanks again for your assistance on this issue.

Another question I have is the effect of temperature on ph, it seems like the ph drops a fair amount when I leave the probe in the cup of tub water for a long period of time. Does the fact that I maintain my tub at 102 make a material difference from the 100 which Nitro assumes in his article.

[denvertub]

Oh, and yes I use Dichlor (about 12 tbs) over the first month after set up... that consistently get me to about 30 cya.

[chem geek]

Thanks for your reply Richard!Interesting... When I plug 500 gallons into the pool calculator I arrive at 28 oz borax by volume to arrive at 50 ppm borates. That's what I've been using for the past 5 years. How did you come up with your calculation? Assuming you are correct, should I replace some water to lower borates? ... and how might the higher borate level effect the other measurements?Anyhow, the problem that I'm having is that TA drops too much when I add enough acid to bring me to my target ph. I've been using a properly calibrated Milwaukee digital ph meter that I happen to have for my marine aquarium. I just used the Taylor color test kit as well and they're both close enough such that I think I have a proper ph reading. After a few tries raising the water to about 100 ppm TA and lowering with acid while aerating, I just tested again and I'm at about 7.7 ph and about 45 ppm TA. Tub is at 102 degrees. Based upon Nitro's article, I should be at 7.6 ph and 80 ppm TA with CH at 150. Thanks again for your assistance on this issue.Another question I have is the effect of temperature on ph, it seems like the ph drops a fair amount when I leave the probe in the cup of tub water for a long period of time. Does the fact that I maintain my tub at 102 make a material difference from the 100 which Nitro assumes in his article.

We are both right, but looking at different chemicals. I was referring to "boric acid" while you were referring to "borax". With 20 Mule Team Borax, you have to add acid since borax raises the pH significantly. With boric acid, it's only slightly acidic so is generally easier to use. Up to you, though. If you do go with the borax and acid route, split the dosage into thirds or fourths and add in an alternating fashion to not have the pH swing too wildly.

Ignore the 80 ppm from Nitro's article. That should be updated to say 50 ppm TA as a target and using 50 ppm Borates as not optional. If you try and have the TA be higher, the pH will tend to rise too quickly. You may still have the pH rise at these levels, but hopefully not as quickly and not requiring as much acid to compensate. And yes, when you add acid, the TA will drop over time. There's not much you can do assuming you've already got the TA low and you target a higher pH, say 7.8, before you do anything to lower it.