Amount of acid Varies; Conflicting Info Between Poolmath & Pool Calc

[just4747]

I see many other threads here asking similar questions but the answer is usually that the person forgot to add TA or borate amounts. I believe I have everything set correctly and am still getting confusing/incorrect numbers.

I am trying to get my pH from about 8 down to 7.6 or so. In Pool Math, in the pH page, I fill in current pH as 8, target as 7.6, TA is 80 from a previous test, borates as 0 since I don't add them (and haven't measured them). Pool Math says to add just 10oz (1 cup and 2 oz) of the muriatic acid I have, which is 31.45% - 20° Baume. I measured 10 fl oz of acid in a measuring cup (just to confirm, they do mean FL oz of volume even though the app says "oz" right)?)

I added the 10 fl oz. in front of a return jet yesterday evening and today, the pH color looks about the same in the TFT tester block - maybe ever so slightly lighter but def not as low as 7.6 or even 7.8. Filter ran all night and I even swirled the water around with a brush right after adding the acid just in case. I've attached pics of my test block which I am interpreting as about 7.9-8.1 somewhere. I used just 3 drops of phenol red.

But, when I check in the Pool Calculator Effects page, it suggests adding 20 fl oz to lower pH by .4...which is double the amount that Pool Math said.

Which am I to follow? Why would they be different if they use the same code and calculations? I made sure that both apps have the same current test results and pool specs.



Current chemistry, if it matters (pool specs in my profile/sig):

 

[mknauss]

Go into settings and turn off Track Borates.

I entered your data as you show and PoolMath shows adding 42 oz of 31.45% muriatic acid to lower the pH from 8 to 7.6.

Update. I get 10 oz. Which makes more sense.

 

[just4747]

Go into settings and turn off Track Borates.

I entered your data as you show and PoolMath shows adding 42 oz of 31.45% muriatic acid to lower the pH from 8 to 7.6.

I keep borates on so I can get CSI calculation even though I don't add them. Won't it stop calculating if I take away borates?

I turned it off just to see and it is still telling me 10 oz, so what's different? What am I missing? You have all my pool size and specs plugged in and everything?

See here:

 

[mknauss]

Turn off Track Borates. Not needed. You do need to Track Temperature for CSI.

I updated my post above. 10 oz is the correct amount.

Be careful using Effect of Adding with Acid and pH adjustment. It is an approximation, at best.

 

[just4747]

Turn off Track Borates. Not needed. You do need to Track Temperature for CSI.

I updated my post above. 10 oz is the correct amount.

Be careful using Effect of Adding with Acid and pH adjustment. It is an approximation, at best.

Understood, but why would Pool Calc's Effects page be off? I use it from time to time and it's always been pretty much the same as Pool Math's suggestions.

Either way, why is my pH still barely any lower, if at all then? Assuming I am reading my block pretty accurately?

Is it possible the pH adjustment with muriatic acid does not take sometimes?

 

[SecoSteve]

Your Ph may have been over 8. Could have been 8.2 or higher, so the 10oz didn't lower it to what you thought.

 

[just4747]

Your Ph may have been over 8. Could have been 8.2 or higher, so the 10oz didn't lower it to what you thought.

Even though the color shade was more on the pink side than red, it wasn't quite as pink as the 8.2 square of the block (color shade not saturation). Though I'm sure the block isn't perfect...

Would you agree that the block in my screenshots above are reading about 7.9-.8.1 today?

 

[SecoSteve]

You could try to lower it again with another 10oz. When you go from 7.5 to 7.2, you really see the difference.

 

[cwswifty]

I added the 10 fl oz. in front of a return jet yesterday evening and today, the pH color looks about the same in the TFT tester block - maybe ever so slightly lighter but def not as low as 7.6 or even 7.8.

If you want to check that your adding the correct amount of MA to achieve your target you should re-check the pH 30 mins after addition (not the next day). With that said, I have found the Orenda app to be more accurate for MA addition calculations.

 

[blazer58]

“I used just 3 drops of phenol red.“
I thought 5 drops should be used

 

[mknauss]

Is it possible the pH adjustment with muriatic acid does not take sometimes?

No. Acid is immediate once well mixed.

I see your initial pH as 7.8 or a bit lower. 8 and above shows as purple in hue to me.

 

[just4747]

“I used just 3 drops of phenol red.“
I thought 5 drops should be used

There are other threads including one from myself asking how to make it easier to read the comparator block...and it was suggested to use less than 5 to get the saturation closer (lighter) to the comparison column, which is ok since all you really want to compare is the color hue, saturation/darkness shouldn't matter.

 

[just4747]

No. Acid is immediate once well mixed.

I see your initial pH as 7.8 or a bit lower. 8 and above shows as purple in hue to me.

The pic of the block above is actually from today after I re-tested the pH but yesterday it was very close, maybe slightly more pink. In person, it is clearly more on the pink side than red so to me that means it must be higher than 7.8 which still shows as more in the red hue than pink on the comparison column.

 

[mknauss]

pH is just not all that critical for your situation. As long as it is not very high, or very low, it does not make much difference. You have a vinyl pool with low CH levels.

 

[just4747]

pH is just not all that critical for your situation. As long as it is not very high, or very low, it does not make much difference. You have a vinyl pool with low CH levels.

I know, but pH went up slowly over weeks so want to adjust it now before it's well above 8.
I'll just add another 10oz of acid and see what happens. Thanks.

 

[just4747]

Another 10oz of acid seems to have gotten the pH down to around 7.6, so that worked.
Thanks all.