Why am I having to add acid

macgas

Active member
Jul 29, 2010
38
Houston,TX
I have a 17000 gal pool with spill over spa, ozonator, jug dumping, 50ppm of borate. The pool looks great, perfectly clear but my pH keeps drifting to 7.8. I have some iron staining so am trying to keep pH a little closer to 7.5. I am having to add about a quart of acid every week to get the pH down to 7.5. It stays there a few days and drifts back up to 7.8. I could understand if I had SWG but I don't. What's up with my pool?

On 8/23 FC 4, CC 0, pH 7.8, TA 150, CH 360, CYA 70, Added 1 gal of 10% chlorine, 1q 1cup of Acid. Goal is FC 5-10
On 8/28 FC 7.5 pH 7.8

TA is elevated I think because when we swim we run the waterfall. Since I live in swampy Houston I think CYA and CH will come down with all the rain we get. Trying not to do a partial refill because of the borates. BTW with the borates the water looks like glass.
 

bk406

Well-known member
Dec 3, 2009
2,690
Central Massachusetts
The waterfall really doesnt have anything to do with the TA being high. Two things are contributing to your pH drift.

1) Your TA is too high. You should try and get that down to 100 or so.

2) The waterfall is aerating the water. Aeration will cause the pH to rise as well due to the outgassing of CO2.

You should lower the pH to around 7.0- 7.2 with acid, then aerate the water to increase the pH. Keep doing this cycle until the TA is down to around 100, and the pH rise should stabilize.
 

Sportsman

Well-known member
Jan 27, 2010
233
Central Valley, CA
**disclaimer: noob trying to help **

bk406 posted while I was replying so condensed.

My TA is down to 150 after a 2 gallons of MA and my pH goes from 7.2 to 7.8 in about a week without aeration.

When you use MA for pH, your TA will slowly go down. You don't have to worry about different procedures.
 

anonapersona

TFP Expert
LifeTime Supporter
Nov 5, 2008
2,598
Do test your tap water to find out what the TA is. If it is high like mine (340) you will find that even small additions of tap water will increase TA some and that means you will need to continue to lower pH and TA with acid.
 

macgas

Active member
Jul 29, 2010
38
Houston,TX
My waterfall is about 7 tons of moss rock, so the water flows over a lot of flat surface and gets pretty well aerated. If I lower pH to 7.0, how long would I have to aerate to bring the pH back up?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
22,069
San Dimas, CA (LA County)
If you run things so the water is really churning, a couple hours ought to do it. When I need to lower TA, I get the spa going 100% and sometimes even run the booster. The spa appears to be boiling, and I've dropped 30 ppm in as little as 5 hours.

Lowering TA by this method will use just as much acid as the way you've been going, it's just faster.
 

anonapersona

TFP Expert
LifeTime Supporter
Nov 5, 2008
2,598
When I did this quick method to lower TA I always wondered after the fact if it contributed to the sand that falls off the moss rocks in my waterfall. I don't know how much depth of rock can decay away before the whole darn thing has to be torn down and rebuilt.

So, mu suggestion would be to not run the waterfall, at least then you won't have that worry. Running the spa and the bubbles there ought to help a lot, as long as you keep the circulation going from the spa to the pool to keep it all mixing well.

Or, just do it slowly, every time you test, add MA to get to 7.2 pH and circulating through the spa to take advantage of that spillover. TA drops by 10 points every 2nd or 3rd time I do that. Then of course when I add tap water it goes back up some.