Bleach Raising my pH

[quincy915]

Yes, when we used pucks and dichlor, rarely added muriatic acid. The brand of OTC bleach I use is HEB, 8.25%. Older posts on TFP attempting to explain the lye amount differences, say between Clorox brand and HEB, made no sense to me. I even searched and read up on MSDS, etc of the bleaches. I tried using Clorox brand for a while, but frankly I felt it sanitized less. Clorox does not seal their bottles! If you know the answer to which OTC has less lye, I'll be happy to be informed.

Since using bleach, my pH rise has been a constant struggle. I have had mod scale on tile since I began learning the BBB. I'm a little better. Say my TA is at 70, I find the pH climbs to 8.0. I try to gently add a little acid. Bamn, my TA is now lower. That's why I add soda. Posts say acid drops TA harder than soda raises pH.

There is a spillover. Very low drop, especially now with a lot of evaporation. Am running pool 24hr at 1250rpm. When I add bleach at midnite, I run rpm higher for about 3 hrs. My pool is old construction. Two jets on south side, one on north in shallow end. There is poor circulation to the south deep end - where in the past I always got algae. North deep end has skimmer basket. Once temps got in the 90s and up, I increased to 24hr and my pool has been clear again.

Pool was re-plastered early 2000s. (On signature) There is still black algae spots, not increasing, which I plan to attempt to eradicate in the fall or winter when I can SLAM and there is less FC demand. My CC is 0 ?? I do brush with metal because of the black algae and a very coarse diamond brite plaster.

Test results:

FC 4
CC 0
TA 80
pH 8.0
CH 340
CYA 70

Lastly, we were told to keep the TA closer to 90-100 with diamond brite plaster by the installer. I'm just trying to keep TA above 70! Any thoughts?

 

[JVTrain]

A few things. Your CYA is a bit high for a manually chlorinated pool but certainly manageable. At that CYA, your FC should always be 5 or above. Keeping your FC in this range should allow you to lessen your pump run time and prevent algae as you keep up with the brushing in problem circulation areas or attempt to reconfigure return direction and improve flow to that area. Could one of the deep end returns be aimed downward to increase flow to the problem area while keeping the other one aimed for surface skimming?

The important number to watch on a plaster pool is the overall CSI number. With the spill over there is additional aeration, plus running the pump 24/7 means you're always aerating. I would allow the TA to drop to 60 and see how your pH responds. Carbon dioxide outgassing is slightly slower at higher pH levels. With pH between 7.6 and 7.8 and a TA of 60 ppm, your CSI index is basically neutral or slightly negative in the safe range. Unless you NEED to keep the TA at 70 or above for warranty reasons from the installer.

 

[elwood58]

I agree that aeration is driving your pH up. Let TA get as low as 60, and only make minor downward adjustments in your pH.

 

[chem geek]

Posts say acid drops TA harder than soda raises pH.

This is absolutely positively not true. Please give links to the posts that say this and I will go back and add correction posts so that others don't get similarly confused by this. Soda Ash raises BOTH pH and TA and raises TA by MORE than acid lowers it so if you were to use a combination of acid and soda ash you would end up increasing TA just as if you were adding baking soda. The following chemically shows the result:

HCl + Na₂CO₃ ---> NaCl + NaHCO₃
Muriatic Acid + Soda Ash ---> Salt + Baking Soda

Adding a little acid only lowers TA a little. The relationship between adding acid and lowering TA is a fixed one. In 18,000 gallons, 46 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) will lower the TA by 10 ppm.

So you should keep your TA lower in spite of what your installer said. You would compensate for the saturation index by having a higher CH instead and a higher pH target of 7.8. However, if you were to have a 70 ppm TA with a pH of 7.7 to 7.8 and your 340 ppm CH, then that is already a near zero balanced Calcite Saturation Index (CSI). If you were to go lower with your TA to 60 ppm, then you could raise your CH to 500 ppm to compensate, but I'd only do this after you get your pH under control.

When you were using Trichlor and Dichlor you WERE adding acid -- it was in those products since Trichlor is very net acidic and even Dichlor is net acidic when accounting for chlorine usage/consumption. In your 18,000 gallon pool, one 3" 8-ounce puck of Trichlor not only adds 3.1 ppm FC and 1.8 ppm CYA, but after the chlorine is used/consumed it is also equivalent to adding 12.6 fluid ounces of full-strength Muriatic Acid. Adding 13.2 ounces weight of Dichlor also raises the FC by 3.1 ppm but the CYA rises by 2.8 ppm and this is equivalent to adding 9.1 fluid ounces of full-strength Muriatic Acid.

The spillover is the likely source of aeration that is increasing carbon dioxide outgassing causing the pH to rise. Having a lower TA and higher pH target lessens that. I would at least temporarily see what happens at a lower TA of 70 ppm, then 60 ppm, to see if you notice any difference, but do not lower the pH below 7.6. When it hits 8.0, lower it to no lower than 7.6. If you find that the lower TA level is helping, then as I wrote above you can compensate to increase the saturation index to protect your plaster by increasing your CH as needed.

In spite of your poor circulation, I think you might be better off running 14 hours a day but spacing out the circulation time into a schedule such as the following:

10AM - 2PM 4 hours
4PM - 7PM 3 hours
10PM - 2AM 4 hours
5AM - 8AM 3 hours

To handle the areas with poor circulation and for better skimmer action you may want to run the pump at higher speed during part of the time, say for an hour or two during the 10AM - 2PM window or the 4PM - 7PM window depending on when you typically have wind blowing debris into the pool.

Finally, after getting the pH target and TA settled (and CH), you can consider using 50 ppm Borates for additional pH buffering.

 

[quincy915]

Okay, then. I'm willing to try. This is a lot to learn and be responsible for....

 

[chem geek]

Just take things one step at a time and see how each stage goes before moving on. You may find that just doing one thing is enough and can stop there. We're here to walk you through this every step of the way.

 

[quincy915]

Thanks