Bleach/borax And Ph

[jeffr72]

I wanted to share my recent experiences with the bleach/borax method and Ph.

Purchased a 225gal HS tub this summer and after much reading wanted to limit the dichlor(cya) and try the bleach method. Due to the tub size and bather load we were changing water every 30-40 days which makes it easy to try different things.

With each of the water changes, calcium hardness was set at ~120ppm, FC varied from 2-6ppm and 2 tbls MPS was added weekly.

The first attempt was with bleach without borax and an initial week of dichlor to establish some cya. This was a total disaster. Each day I added 3.5oz Clorox. TA varied from 80-100ppm, Ph swings were violent and I quickly discontinued.

On the next water change, I tried 20 Mule Team Borax (10oz ~40ppm). Added about 1/2 Borax, 2tbls acid (sodium bisulfate) then repeated. Needed a bit more acid to balance, TA came in at about 60 and Ph at 7.6 After about a week of dichlor, numbers had dropped a little to 50 and 7.4 CYA was ~60ppm. I felt the numbers would climb when I started adding bleach and left them alone.

Over the next three weeks I added 3.5 oz of Clorox each day. I tested the water almost every day (more in the beginning) and to my surprise the Ph and TA actually dropped over time. The Ph about .1 per week and the TA about 5ppm per week. I ended up adding baking soda and borax twice over the 3 week period to bring the water into balance. Needless to say I was quite impressed with the stability of the borax.

I just did another water change and am trying a 20% decrease in borax. Numbers came in at TA 60 Ph 7.6 when all was settled. Will report back next month with the results.

jeff

[chem geek]

Jeff,

Thanks for the update. The Borates definitely dampen the pH swing when bleach is added and then used up. A higher bather load will result in much higher pH swings since you need to add more chlorine for that higher bather load.

In your situation, 3.5 ounces of 6% bleach in 225 gallons would raise the Free Chlorine (FC) by 7.5 ppm (if you were adding it soon after a soak, then the chlorine may have quickly combined with ammonia to form Combined Chlorine -- not sure why you only measured 2-6 ppm). With a TA of 80 ppm and CYA of 30 ppm, the pH would rise from 7.5 to 8.0 with that bleach addition. With the higher TA, the pH may or may not have dropped over time and you may have needed to add some acid. The weekly MPS could have kept the pH more in check if it wasn't pH balanced (normal MPS is acidic), but I would expect the TA to drop over time. So something seems missing in your description in the no-Borates phase. With acidic MPS addition, the TA should have dropped over time (measured at the same pH, so after adjusting for pH if necessary).

The 10 oz. of 20 Mule Team Borax is around 40 ppm as you said, but I calculate that you would have needed about 4.6 ounces volume (about 9 tablespoons) of dry acid to balance the pH with that amount of Borax. A week of Dichlor at 7 ppm FC per day is 1.5 ounces weight (about 3 tablespoons) cumulatively added over that week (that's 18 teaspoons, so around 2-1/2 teaspoons per day). The pH would go down were it not for outgassing, but the TA does indeed drop by 9.7 ppm so that makes sense. So it does sound like your pre-Borates situation had more pH rise from outgassing. Now, with 40 ppm Borates, when you add 3.5 ounces of bleach, the pH would rise from 7.5 to 7.7 (or 7.6 to 7.8) which is less of a jump.

The pH dropping over time is not surprising since your TA is now lower. I don't think this has to do with the Borates, but rather from the combination of weekly MPS addition, which is acidic and makes pH and TA drop, along with carbon dioxide outgassing which makes the pH rise. It seems that your stable pH balance would be closer to around 70 ppm TA. However, the MPS addition would cause your TA to drop in any event (again, not sure why you didn't see that before the Borates). If you plan to continue to use MPS weekly, then you'll have to add baking soda to keep the TA up (but not too high -- sounds like 70 ppm is the highest for best pH stability in your situation). Do you find that your pH drops from 7.6 to 7.2 (and the TA drop by 8 ppm) after you add the MPS? If not, then perhaps it's more pH balanced in which case the TA won't drop as quickly over time.

Richard

[jeffr72]

The pH dropping over time is not surprising since your TA is now lower. I don't think this has to do with the Borates, but rather from the combination of weekly MPS addition, which is acidic and makes pH and TA drop, along with carbon dioxide outgassing which makes the pH rise. It seems that your stable pH balance would be closer to around 70 ppm TA. However, the MPS addition would cause your TA to drop in any event (again, not sure why you didn't see that before the Borates). If you plan to continue to use MPS weekly, then you'll have to add baking soda to keep the TA up (but not too high -- sounds like 70 ppm is the highest for best pH stability in your situation). Do you find that your pH drops from 7.6 to 7.2 (and the TA drop by 8 ppm) after you add the MPS? If not, then perhaps it's more pH balanced in which case the TA won't drop as quickly over time.

Richard

Hi,

I never gave it a thought that MPS would affect the balance. I assumed it was neutral. Will watch and let you know.

Thanks again to you and everyone else that contributes in this forum. I never would have succeeded with the bleach method without all your help.

jeff