Another Borate Question

[cofive]

I have a TA of about 50-60 in an attempt to hold my Ph in the 7.4-7.6 range. I've seen the advice that with low TA the addition of borates is helpful and will also buffer the Ph. My question is, will the borates buffer the Ph rise due to the use of bleach in the dichlor/bleach method? I am finding that my Ph creeps each week and I have to add about .5oz of Muriatic Acid to bring it down. Other than this creep, I am sworn to the dichlor/bleach method, it's easy and inexpensive. For the record I also found the CYA reduction does happen per month, so I use dichlor for a few days (10ppm) once a month.

Ken

[chem geek]

The borates will reduce the rate of pH rise, but won't reduce the amount of acid needed to bring the pH back down. Only lowering the TA (and reducing aeration) will lower the amount of acid needed, at least from carbon dioxide outgassing. Are you using 6% Clorox Regular bleach or are you using another brand? Clorox Regular has the lowest amount of excess lye in it. If you are using another bleach, it may have more excess lye thereby requiring you to add acid now and then. Adding acid once a week isn't a big deal (and eventually you'll need to add baking soda as the TA will drop slowly over time as well), but you may be able to reduce this problem by switching to Clorox Regular if you haven't done so already (note that in Canada it's Clorox Ultra that is the 6% bleach).

[quantumchromodynamics]

I have a TA of about 50-60 in an attempt to hold my Ph in the 7.4-7.6 range.

A certain percentage of the bicarbonate alkalinity will convert into carbon dioxide. The percent of the bicarbonate alkalinity that becomes carbon dioxide is dependent on the pH.

Here are some values of the percent of bicarbonate ion that become carbon dioxide.

pH..........% Carbon Dioxide

7.0.............18.3

7.1.............15.1

7.2.............12.4

7.3.............10.1

7.4...............8.2

7.5...............6.6

7.6...............5.3

7.7...............4.3

7.8...............3.4

7.9...............2.7

8.0...............2.2

As you can see, there is 2.41 times as much carbon dioxide in the water at a pH of 7.4 as there is at a pH of 7.8.

This is why there is less pH rise when you use a higher pH even though it might seem counter-intuitive.

Keeping your pH at 7.4 to 7.5 is causing your pH to rise at a much faster rate than if you kept it at about 7.7.

I think that you will experience a much more stable pH if you target a pH of 7.6 to 7.8 instead of 7.4 to 7.6.

[cofive]

The borates will reduce the rate of pH rise, but won't reduce the amount of acid needed to bring the pH back down. Only lowering the TA (and reducing aeration) will lower the amount of acid needed, at least from carbon dioxide outgassing. Are you using 6% Clorox Regular bleach or are you using another brand? Clorox Regular has the lowest amount of excess lye in it. If you are using another bleach, it may have more excess lye thereby requiring you to add acid now and then. Adding acid once a week isn't a big deal (and eventually you'll need to add baking soda as the TA will drop slowly over time as well), but you may be able to reduce this problem by switching to Clorox Regular if you haven't done so already (note that in Canada it's Clorox Ultra that is the 6% bleach).

Yes I'm using 6% Clorox and getting a drift from the 7.4 to 7.6 range into the 7.8 range. I will also take the advice from QCD and i'll shoot for the and maintain the 7.6 to 7.8 range. Not a big deal adding the .5oz of acid on occasion, just was curious.

Ken