Alkalinity Keeps Dropping

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L

Lawtyger

Well-known member
Mar 11, 2016
121
Tampa, Florida
Hi everyone! I have a situation where my alkalinity seems like it has continually dropped over the last couple months (November until present) and I’m not sure what is going on. The pool was finished in March of 2016 and from March 2016 to November 2016 I don’t recall having to increase the alkalinity once. However, since November 2016 the alkalinity doesn’t want to stabilize.

Some other things to consider that may be relevant:

  • I still feel like I’m an trying to get a good feel for doing the pool chemical readings, etc. myself – I enjoy it but when things like this pop up I feel like I’m screwing up somehow.
  • I had a mustard algae issue in early November which required a shock and around January 1st while cleaning the filter I had some concerns that I never fully got rid of all the algae based on the greenish coloring in the filter so I shocked the pool again.
  • You’ll see two of the readings below were from Pinch A Penny and I have no faith in the numbers they provided.
  • I think I still have some issues with my own readings when testing something like alkalinity and the test results seem to fall between two readings (for example, between 80 and 70, etc.).
  • The most recent addition of baking soda to increase alkalinity was done on January 2nd and you’ll see how my alkalinity has dropped over just a few weeks so that may be the date you want to look at below first.

Below are my pool readings from mid-December until the present. Any idea what I am doing wrong or how to stop the alkalinity from decreasing so quickly? Totally lost and confused at this point. At least baking soda from Sam's is relatively cheap I suppose, lol.

Dec 11, 2016
Total Alkalinity: 60.00 ppm
pH: 7.70
Free Chlorine: 7.00 ppm
Salt: 2900.00 ppm

Dec 13, 2016
pH: 7.70
Free Chlorine: 6.00 ppm

Dec 16, 2016
Total Alkalinity: 100.00 ppm
pH: 8.00
Free Chlorine: 4.00 ppm
Stabilizer: 100.00 ppm
Calcium Hardness: 280.00 ppm
Salt: 3100.00 ppm

Readings done by Pinch A Penny - Added 5 pounds of ALK increaser per their suggestion.

Dec 17, 2016
Total Alkalinity: 90.00 ppm
pH: 8.20
Free Chlorine: 5.00 ppm

Dec 18, 2016
Total Alkalinity: 80.00 ppm
pH: 7.40
Free Chlorine: 5.00 ppm

Dec 19, 2016
Total Alkalinity: 100.00 ppm
Calcium Hardness: 300.00 ppm
Salt: 3300.00 ppm
Free Chlorine: 4.00 ppm
pH: 7.60
Stabilizer: 100.00 ppm

Readings done by Pinch A Penny.

Dec 21, 2016
Free Chlorine: 9.00 ppm
pH: 7.60

Dec 23, 2016
Total Alkalinity: 80.00 ppm
Free Chlorine: 10.00 ppm
pH: 7.70

Dec 24, 2016
pH: 7.50

Dec 26, 2016
pH: 7.90
Free Chlorine: 8.50 ppm

Dec 28, 2016
pH: 7.60
Free Chlorine: 7.50 ppm

Dec 30, 2016
Free Chlorine: 6.00 ppm
pH: 7.80

Dec 31, 2016
pH: 7.40

Jan 2, 2017
Total Alkalinity: 70.00 ppm
pH: 7.60

Treatments:

  • Added 8 lbs. of baking soda.
  • Added 2 and ½ gallons of liquid chlorine.

Jan 3, 2017
Total Alkalinity: 120.00 ppm
pH: 8.00
Free Chlorine: 16.00 ppm

Jan 4, 2017
Total Alkalinity: 110.00 ppm
pH: 7.50

Jan 5, 2017
pH: 7.60

Jan 8, 2017
Total Alkalinity: 90.00 ppm
pH: 7.60

Jan 9, 2017
Total Alkalinity: 90.00 ppm
Free Chlorine: 12.00 ppm
Calcium Hardness: 300.00 ppm
Stabilizer: 60.00 ppm
Salt: 3300.00 ppm
pH: 7.80

Jan 11, 2017
Total Alkalinity: 90.00 ppm
pH: 7.70

Jan 14, 2017
Total Alkalinity: 80.00 ppm
pH: 7.60


Jan 17, 2017
Total Alkalinity: 70.00 ppm
Calcium Hardness: 275.00 ppm
pH: 7.70
Stabilizer: 40.00 ppm
Salt: 3400.00 ppm
Free Chlorine: 8.00 ppm
 
I guess I didn't recall that the suggested TA for a SWG pool was 60-80 per the first link you provided above. I recall reading that page early on but was more focused on FC and stabilizer. Basically, my current ALK is just fine then? That was easy, lol.

My readings from yesterday were:
Jan 17, 2017
 Total Alkalinity: 70.00 ppm
Calcium Hardness: 275.00 ppm
pH: 7.70
Stabilizer: 40.00 ppm
Salt: 3400.00 ppm
Free Chlorine: 8.00 ppm

After adding acid yesterday my pH is now at 7.4.
My FC has been dropping on it's own (I haven't had my SWG on in weeks) and I'll target 5.
Looks like I need to get my CYA up to 70 - given how slow my FC has dropped should I increase CYA? I was thinking my FC taking so long to lower on its own may have been a result of the current CYA keeping FC from burning off.
 
Thanks main reasons for lower FC consumption this time of year is lower water temps and less sun due to shorter days. No need to increase cya now, waiting until spring is fine.

Yes, your TA is just fine. Easy! :) It is also fine to let your pH hang out at 7.8 and lower it to 7.6 when it gets to 8.0.
 
pooldv said:
It is also fine to let your pH hang out at 7.8 and lower it to 7.6 when it gets to 8.0
Click to expand...

Good info. Just to be sure I understand, what was the number you said I could let the pH hang out at? I assume there is a range you were suggesting or a specific number but you typed 7.i. From the link you sent it says "when it climbs to 7.8 add acid to lower it back to 7.2-7.5 (This is also IMPORTANT!)." Just making sure you weren't suggesting something different.
 
Can someone explain why TA needs to be 60 - 70 in a salt pool. My fill occurred in August and the PB has been managing since then. At Christmastime I checked my TA with a small kit I bought at ACE and the TA was 30. My salt has risen from 3400 to 4300 based on readings from my Hayward Aquaconnect automation panel. It seemed to rise as the water temps dropped so I dont know if this is accurate or not. Pool temp at Christmas was 56 degrees F so I dont know if that affects readings or not. FC is good with the pump running 8 hrs each night and salt cell at 5%. PB adds acid each week to control PH as the spa spillover and water features run intermittently during the cleaning cycle and cause some aeration.
 
Acid lowers not only the pH but the TA as well. Chances are the service that's maintaining your pool is targeting a pH that is too low which calls for an excessive acid demand.

Alkalinity is needed in the water to prevent the water from being too aggressive and etching the plaster. A TA below about 50ppm will be difficult to not be overly aggressive and you risk the pH crashing extremely low. 60-70ppm is a nice balance between having an adequate buffer for the pH yet still low enough to limit how quickly the pH will rise.
 
BigEinAZ said:
Can someone explain why TA needs to be 60 - 70 in a salt pool. My fill occurred in August and the PB has been managing since then. At Christmastime I checked my TA with a small kit I bought at ACE and the TA was 30. My salt has risen from 3400 to 4300 based on readings from my Hayward Aquaconnect automation panel. It seemed to rise as the water temps dropped so I dont know if this is accurate or not. Pool temp at Christmas was 56 degrees F so I dont know if that affects readings or not. FC is good with the pump running 8 hrs each night and salt cell at 5%. PB adds acid each week to control PH as the spa spillover and water features run intermittently during the cleaning cycle and cause some aeration.
Click to expand...

My suggestion would be that you get one of the high end test kits we recommend and analyze the water with that. The cheapo test kits don't typically work very well (I've used several) and a TA of 30ppm does not sound right at all. Without knowing any of your other chemical levels it's very hard to make a determination of how aggressive your water is but 30ppm total alkalinity would leave only a very small portion of it as carbonate alkalinity and your pH could easily crash with a TA that low.

Also, having a salt reading increase 1000ppm over the course of 6 months is a lot. It could be just natural measurement error since salt cell readouts are not very accurate BUT Hayward cells tend to be the best for salinity readings. The only way to know for sure would be to have the salt content precisely measured using a Taylor K-1766 salt test kit. That kit measures the chlorine ion (Cl-) level exactly with little to no interference from anything else. It's an exact chemical measurement of salinity as opposed to an inferred measurement from an electronic probe.
 
I notice quite a variation with your chems, especially the day after they were checked. Do you have an autofill? If so I would look into a possible leak. The only way you will see the Alk. fluctuate like that is when water has been lowered and filled back up. Also, my suggestion in regard to your chems would be to use chems that are pool specific. This is because when you buy Baking Soda, for instance, you might get other dissolved solids, perfumes, and other non-specific pool contaminates added without being aware.
 

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The most common reason for fluctuation in the TA test is testing error. You are at the mercy of pinch-a-penny to manage your pool water and time and time again over the years, we see poor testing as the problem

You own good test kit will provide you accurate results and keep you from having these fluctuations which probably don't exist.

Reed'spoolservice,

Baking soda has proven to be a Very acceptable product for raising TA. We promote the use of alternative products that are often less money but do the same thing. We like to use 20 Mule Team Borax for raising pH, Clorox is exactly the same as pool chlorine (although not always cheaper) and we like muriatic acid for lowering pH.

Read read "The ABC's of Pool Water Chemistry" up in Pool School.......it'll give you some insight as to what we teach.
 
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