Bleach and acid

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emdemd77

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Jun 28, 2011
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I am a new pool owner, and I have just switched to using bleach in my pool due to my CYA being at 90. I noticed after adding bleach my PH goes up, and I looked up the PH of bleach and what do you know - it has a high PH. So, is it normal to have to add acid every time I add bleach? I have been adding about 90 oz each day to my pool which is bringing my PH up to around 7.8. Then, I have been adding about 1.5 to 2 cups of acid to keep bringing my PH back down to 7.6. My TA is hanging around 120. I did measure it at 100 the other day after adding acid, but today before my dose of chlorine it was 120. My pool is approximately 18,000 gallons.


I read somewhere that bleach only increases the PH temporarily because acid is produced as chlorine is used up. Is this true and am I just being too quick to add acid? I do think I am a little jumpy because I had that yellow mustard algae already and I am trying to avoid that again.

Thanks,
Erin
 
Welcome to TFP!

Bleach is alkaline, but not so much so that a simple 90 oz. bleach addition should put your pH out of recommended limits (7.2 to 7.8). Since your TA is 120, it should probably come down some. Lowering the TA will allow your pool to buffer the pH rise from chemical additions and other things. Here's how to lower your TA...pool-school/lowering%20total%20alkalinity.

What kind of pool do you have? If it is inground plaster, how old is it? Any chance that you have a SWCG?
 
I read somewhere that bleach only increases the PH temporarily because acid is produced as chlorine is used up. Is this true and am I just being too quick to add acid?
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Absolutely. Leave your pH alone. Bleach ends up being pH neutral.

You didn't ask, but your biggest issue (and probably why you had mustard algae) is your CYA is too high. You will have a much more manageable pool if you drain some water and reduce CYA to around 50-60ppm.

At what level are you keeping your chlorine?
 
When you add bleach the PH goes up, and as the chlorine gets used up the PH goes back down again. The net effect is almost exactly PH neutral (there are often extremely small PH increases, too small to measure or notice). In routine usage the FC level remains more or less constant, so you never notice the temporary PH increase when FC goes up.

Another thing that can affect the situation is when you are raising the FC level quite high the PH test can be wrong. The PH test tends to read higher than actual when FC is above 10, an effect that increases as the FC level continues to go up. It is best to ignore the PH test while FC levels are above 10 because of this.
 
I love this forum! Thank you for the replies!

I have an inground gunnite pool, but I really have no idea how old it is. The house was built in 1982. So the pool could have been built in the 1980s or 1990s. It does not look any newer than that. Is an SWCG a salt water pool? I do not have that.

I shocked the heck out of my pool after the mustard algae and it has looked great. I say "the heck out of it" because my CYA is so high that I really had to bring up the chlorine level. Yikes. The problem was created when I let the chlorine drop below 1 ppm when we were out of town. Will really try to avoid repeating that mistake in the future. Regarding the chlorine level, I have been keeping it between 2.5ppm to 4ppm, or so my test kit says. I know that I am supposed to keep it higher, but it seems like I already add so much chlorine. Could there be something else interfering with my chlorine reading? We have trees, and so we clean the leaves out of the skimmer daily and run the pool cleaner every other day. Some days it windy and we have lots of leaves, some days it's not so bad.

I have been trying to keep the PH down because I read that chlorine more effective at lower levels. And with my CYA level so high, I want my chlorine effective. How do I know my true PH if the chlorine interferes with the reading? I may try bringing the TA down around 100 this weekend. Funny it was 80 about a month ago and the guy at the pool store told me I needed to add 10 lbs of alkalinity control. I checked online and that seemed way off, so I added half and topped off my pool to bring it to the 120 range.

Assuming my PH reading is correct (big assumption maybe), should I try to bring it down to around 7.4 and hope that it will float more between 7.4 ato 7.6 instead of 7.6 to 7.8. Will adding Borax help in addition to bringing the TA down? I bought some at the store, but have not added any.

Btw, regarding my high CYA. I was hoping to make it through the season without a partial draining my pool. I live in the Austin, TX area so my ideal CYA level would be on the higher side of the range, right? Would 60 be ideal? The pool store guys are not concerned about my CYA at 90 - go figure. And still say my chorine should be maintained at 3 to 5. Thanks everyone!
 
What is your FC level? That has a large influence on how reliable the PH test is.

Yes, a SWG is a salt water chlorine generator, sometimes referred to as a salt pool.

It is better to have PH around 7.5 to 7.8, rather than 7.4 to 7.6. Chlorine being ineffective at high PH is only really true when you aren't using any CYA at all. With CYA in the water any reasonable PH (7.2 to 7.8) is more or less the same as far as chlorine is concerned.

We recommend CYA be between 30 and 50 in most parts of the country. With CYA around 90 you can get by, but recovering from algae is a major pain.
 
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