TA vs acid demand

dschlic1

LifeTime Supporter
Oct 5, 2007
560
Valrico, FL
#1
This might be a topic for chemistry 101, but am putting it here because I am a newie. My pool for several reasons has an acid demand. This means that every so often (usually once a week) I have to add acid to the pool to lower the pH. However in doing so I also kill by total alkalinity level. Friday night I dosed my pool with acid. Saturday morning my readings: (I added a bit too much acid this time)
FC 3.7
TC 3.8
CC .1
pH 6.9
TA 22
CH 281

I added 8 lbs of baking soda and Sunday morning:
FC 3.3
TC 3.5
CC .2
pH 7.5
TA 86
CH 276

So my question is I am going to have to add 8 to 10 lbs of baking soda every time I correct the pH on my pool? If so what is this going to do to my TDS?
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
#2
Lowering the PH with acid will lower the TA a little bit, just as raising the PH with borax will raise the TA a little bit. For example, lowering the PH from 7.5 to 6.9 with acid will lower the TA from 86 to 73. What happens when you raise the PH depends on exactly why the PH is increasing. If the PH is increasing because of aeration, such as from a waterfall or SWG, then the TA will not go up. However raising the PH because of plaster curing or adding borax or soda ash will raise the TA back up (plaster curing and soda ash will actually raise it above 86, while borax should put it back to 86).

The net effect is that you will need to add some baking soda every now and then, probably two or three times per season, but not nearly as frequently as you add acid. In the long run this will increase your TDS level, but I wouldn't worry about that. TDS is a misleading measurement. It really matters what particular dissolved solids there are, not so much what the total level of dissolved solid is. As long as you use muriatic acid and baking soda you aren't going to be getting any of the dissolved solids that you don't want and there shouldn't be any problems for a very very long time (or ever if you have some water replacement each season from closing for the winter or splash out).
 
G
#3
dschlic1 said:
This might be a topic for chemistry 101, but am putting it here because I am a newie. My pool for several reasons has an acid demand. This means that every so often (usually once a week) I have to add acid to the pool to lower the pH. However in doing so I also kill by total alkalinity level. Friday night I dosed my pool with acid. Saturday morning my readings: (I added a bit too much acid this time)
FC 3.7
TC 3.8
CC .1
pH 6.9
TA 22
CH 281

I added 8 lbs of baking soda and Sunday morning:
FC 3.3
TC 3.5
CC .2
pH 7.5
TA 86
CH 276

So my question is I am going to have to add 8 to 10 lbs of baking soda every time I correct the pH on my pool? If so what is this going to do to my TDS?
My question is how are you getting these test result readings? Unless you have a $1000 colorimeter there is no way you can have readings with this type of precision and even with that type of equipment some of the tests will have a larger window of precision, sometimes +/- 20 ppm because of the nature of the test itself! If the testing is being done with strips read by a machine then I would not trust them at all! Your water balance might not be changing as much as you think!

Get yourself a good drop based test kit and do your own testing!

New plaster pools always have a large acid demand for the first 6 months to year as the plaster cures. After that it settles down a bit. What form of chlorine are you using? If you are using trichlor or dichlor you will 'eat up' TA faster than if you are using an unstabilzied chlorine because the stabilized chlorines are acidic.

Finally, TA will move up and down as pH moves up and down. You want to get your TA readings when the pH is where you want it, usually 7.6. If the pH is higher or lower then the TA will be also.

TDS is a bogus measurement. Don't even worry about it as Jason said!
 

dschlic1

LifeTime Supporter
Oct 5, 2007
560
Valrico, FL
#4
I just recently purchased a LaMotte ColorQ Pro 7. I know that some people have had problems with these units, however the readings I am getting from it are close the the readings I get from my local pool store and also from some test strips. So three sources of information and all are close.

I have a Goldline Aqua Plus unit with the T-15 cell. This in combination with a new pool and several sources of aeration means that I will always have an acid demand (just greater right now).

I do not intent to have any water replacement as I live in west central Florida. We do not intent to winterize our pool at all, in fact we were swimming in it Sunday! Solar heating is great. :-D
 

JCJR

LifeTime Supporter
May 4, 2007
267
Miami
#5
According to original post PH went from 6.9 to 7.5 from one morning to the next and TA went from 22 to 86.

Does adding baking soda make your ph rise that much so fast?
 

JCJR

LifeTime Supporter
May 4, 2007
267
Miami
#6
Dschlic1,

I also live in FL and I am installing solar panels (this week). Can you please post your Pool temp, ambient air temp and if you can surface sqft, panel sqft.

I have 740 sqft of pool surface and am installing 600sqft of panels (81% of coverage) on a West facing roof.

Just alone with a clear solar cover, I have 82deg water with air temps from 80 high to 60 low. I would love to get an additional 10 degrees from my panels (at least when the temp dips into the low 70s as a High.
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
#7
How much effect baking soda has on the PH is very dependent on the starting TA. Since his TA was very very low to begin with the baking soda had a large effect on PH. If his TA had been higher to start the effect would have been far smaller. For example if he was to add another 8 lbs of baking soda the PH would only go up an additional .2, not nearly as large as the the .6 increase from the first round.
 

dschlic1

LifeTime Supporter
Oct 5, 2007
560
Valrico, FL
#8
JCJR our pool is 242 sq ft and we have 240 sq ft of solar panels on a south facing roof. Sunday our water temp was 81 to 84. We do not have a physical cover, rather use a liquid based blanket. Ambient temperatures last week were in the low eighties. I have been told what is more important is the gulf temperature. Pools tend to follow the Gulf temperature if unheated. I noticed that yesterday the Gulf temperature was in the 60's.
 

JCJR

LifeTime Supporter
May 4, 2007
267
Miami
#9
dschlic1 said:
JCJR our pool is 242 sq ft and we have 240 sq ft of solar panels on a south facing roof. Sunday our water temp was 81 to 84. We do not have a physical cover, rather use a liquid based blanket. Ambient temperatures last week were in the low eighties. I have been told what is more important is the gulf temperature. Pools tend to follow the Gulf temperature if unheated. I noticed that yesterday the Gulf temperature was in the 60's.
If that's the case, I am going to be dissapointed. Like I said, my pool temp has been 82-83 for the last month just using a solar cover. My neighbors pool has been 74-77. I have been averaging 7-8 degrees warmer. I am hoping that I get an additional 8 degrees for a total of 14-16 degree increase from uncovered/unheated pools.

What do you mean by Gulf Temp, and where would I check that temp?
 

dschlic1

LifeTime Supporter
Oct 5, 2007
560
Valrico, FL
#10
We are located on the west coast of Florida (Tampa Bay area). The gulf temperature is the temperature of the Gulf of Mexico offshore. In reality any nearby large body of water will give you the "normal" unheated water temperature.