High Muriatic Acid Consumption

[anthony]

Hi All,

I've been on the BBB Method now since refilling last November. All of the number have come into alignment. Pool water looks great. I haven't seen any algae.

Here are the numbers

~35 ppm CYA
70 ppm TA
260 ppm CH
79 degF Temp
7.5 pH
4.0 FC (Bleach)
0.0 CC
-0.19 CSI (per http://www.poolcalculator.com)

One thing I've been tracking has been Muriatic Acid use. To maintain a constant pH, I need to add about 2 cups of 31.45% Muriatic Acid every other day. I'm wondering if that's normal?

Additional data that may be relevant:
* I do have a Spa with a spillway. The Spa is part of the normal circuit. So, when the pump runs water is flowing over the spillway. I typically run the pump 6 to 8 hours a day.
* In early November after refill, my TA was at 150 ppm. This is the TA in our tap water. Aeration via the spillway and Spa use plus Muriatic Acid has pulled the TA down by 80 ppm over 5 months.
* I'm seeing TA level out now. I suspect it's because the weather is warming up and I'm starting to adding water from the tap more often.
* I am not seeing a decrease in my upward pH drift.
* I have consistently been adding about 2 cups of Muriatic Acid every other day since refill this past November.

Thanks

-Anthony

 

[chem geek]

You would normally see a decline in the amount of acid needed per time as the TA level got lower if the source of pH rise was due to carbon dioxide outgassing from your aeration. Have you tried not lowering the pH as much and see if it slows down in its rise near 7.7 or 7.8? You shouldn't lower the pH with acid below 7.5 since that would just result in faster outgassing and more acid needed. Since your pool was a little over a year old last November, I would think pH rise from plaster would not still be occurring. Have you noticed the CH rising over time?

 

[Richard320]

That sounds about right to me.

Every pool is different.

 

[anonapersona]

I'll guess that your tap water has very high TA. Mine has tested 220 to 340 ppm TA, so when I am adding water to the pool TA goes up over time. Rain water brings TA down if there is enough to matter.

FWIW 3 cups MA every other day or so is pretty normal for me, trying to reduce pH from 7.8 (or 8.0) to 7.5. Sometimes I push toward 7.2 just to work on reducing TA and that may take 6 cups MA or more, depending on just where TA is at the time as acid needed is directly proportional to the beginning TA.

 

[anthony]

Hi Chem Geek,

I had been running my pH around 7.8 during the colder months to maintain CSI. During that time I was still running around 2 cups every other day. In regards to your question on CH, CH has slowly drifted up. I manually raised CH to 220 on 11/23/2013. I measure CH at 240 ppm on 1/30/2014. I'm now in the 260 ppm range. Tap water is around 130 ppm. I've refilled about 3 times this year.

Hi Richard and anonapersona,

Thanks for the feedback.

-Anthony