Carbonate Alkalinity, TA, and pH range for new Pebble Tech pool

[TheMauiBeach]

The pool is coming up on two months old. My numbers at 4:45 pm tonight were FC 3.5, TC 3.5, pH 7.85, TA 90, CYA 70. Still using CH of 210 from a couple of days ago. My CSI is +.23. I have read on TFP that a lower TA would mean less daily pH rise. Last night at 6:30pm, the pH was 7.48 a few hours after adding 42 oz of acid. I added another 24 oz of acid tonight to get the pH down a bit. I will add liquid chlorine around dark.

What do I do about the TA and carbonate alkalinity since it is on the low side as per the Pebble Tech "ongoing maintenance ranges"? The Pebble Tech guidance does say you can be outside of the listed ranges if the LSI is -.3 to +.3. But, the listed range for ongoing maintenance (after 28 days) is a carbonate alkalinity of 80 to 100 ppm, not total alkalinity. With my CYA of 70 and pH of 7.85, the calculated carbonate alkalinity is about 65 ppm. Do I need to get the TA up to have a higher carbonate alkalinity, or let if fall or keep TA around 80 and hope I can get by adding less acid?

Pool Math shows a CSI of -.04 with pH of 7.6, and TA of 85, at 91F. That is what I expect it to be after the 24 oz of acid gets mixed in now. The water is still extremely clear.

My TA had been about 110 until adding 106 oz of acid over the last three nights.

 

[proavia]

Consider lowering the TA to 60-70. That will help slow the pH rise.

What is the pH, TA and CH of your fill water?

An FC of 3.5 with a CYA of 70 is an algae outbreak waiting to happen.
Have a look at the FC/CYA Levels

FC_CYA_lc_chart.jpg

FC/CYA Chart for Liquid Chlorine - Non-SWG Pools

www.troublefreepool.com

Your CYA of 70 is a bit high for a non-SWG pool.

 

[TheMauiBeach]

Thanks for the help.

I added 79 oz of 12.5% chlorine at night, on 8/15. On 8/16 in the evening FC was down to 4.0, so I added another 40 ounces. It sounds like I need to go way over the target, so it never goes below 8-10. I was using the suggested 7.5% of CYA as my target while I figure out how much to add each night. 7.5% is FC of 5.25. I thought I needed to mostly stay over that number. It should be well over that all night and into the day. I haven't had any algae yet... knock on wood. I was planning another partial water change out, to get the CYA down further, but will wait on that to conserve water since it has been SOOO hot here in Houston.

I will check my fill water and post a record of that.

My main concern is with the TA going so low, my carbonate alkalinity will be super low, so is that "bad" for the Pebble Tech surface? Does it matter since it is a new surface?

 

[TheMauiBeach]

My fill water tested at a pH of 7.71, TA of 200 ppm, and CH of 90 ppm. I will retest when I get my TA reagent refill.

I checked my pool water and the acid added earlier has the pH down to 7.61 at 8:45 pm. My CSI now should be -0.04 to -.01 depending on the actual TA drop, but I didn't measure TA so I could use the last of my reagent to test the fill water TA.

 

[pjt]

I was planning another partial water change out, to get the CYA down further

CYA will naturally degrade with summer weather and warm water. By October, your CYA will probably be ~50. Right now, a CYA level of 70 is a little high but manageable for a LC pool.

I would highly recommend installing a SWCG. It's the ideal choice for our climate.

My main concern is with the TA going so low

A TA down to 50 is perfectly fine. With a TA of 50-60, your pH rise will be minimal. Manage the CSI.

 

[pjt]

My fill water tested at a pH of 7.71, TA of 200 ppm, and CH of 90 ppm.

With fill water TA of 200, you will be constantly dealing with increasing TA, especially in the summer. Manage the pH with MA. You'll likely be adding MA 2-3 times a week.

 

[TheMauiBeach]

I did a double check on the fill water TA. It is 200 ppm. I used 2# of cal-hypo last night to get my FC up. My numbers at 7am were FC 11, TC 11, pH 8.19, TA 80, CYA 70, and CH 210, at 86F for a CSI of +.45. The water is crystal clear. My pH is up from 7.66 to 8.19 in 12 hours. That is the biggest change I have ever seen and it occurred in 12 hours while my usual tests are 24 hours apart. Is that likely from the cal-hypo? Does that mean anything else?

I added 48 oz of acid which should drop my pH to 7.66 according to the impact it has had on my pH in the last month. That is more MA than PoolMath shows, but that is what happens in my pool with the MA I have. I did notice that the pool store MA I just got is dated July of 2020. I read that it should still be good. Maybe it isn't quite as good and that is why it is taking more acid. If the MA doesn't drop my TA too much, my new CSI should be -.06. But, it looks like it is going to go up to the high pH very quickly and will be heading back to a higher, positive CSI in 12 hours.

I am working towards the suggestion that the TA can be on the low side, maybe down to 50, but as it is getting lower, my acid demand is going way up from what it was. How do I react to that? If my pH is getting to the 8 range rather quickly, does that mean I will have a scale problem or other issues up to the next day when I test and correct?

 

[mgtfp]

How are you testing pH? With the Taylor drop test the pH readings will show high due to chlorine interference above FC about 10 ppm.

But your values to 2 digits look more like pH meter readings.

 

[TheMauiBeach]

How are you testing pH? With the Taylor drop test the pH readings will show high due to chlorine interference above FC about 10 ppm.

But your values to 2 digits look more like pH meter readings.

I do both. Two decimal pH numbers are from Apera PH60 meter. Single decimal is from the Taylor K-2006 kit which shows color similar to 8.0. I just got the meter in the last week. Just using it so I am more sure of the pH values for getting the water balance figured out.

 

[mgtfp]

Just wanted to check that you don't just have a false high pH reading due to chlorine interference.

The chlorination cycle with cal hypo (as with liquid chlorine or SWGs) is pH neutral. When increasing FC, pH will rise. Once that FC is used up by UV or killing something, pH will be down to where it started. Plus some of pH rise that will have happened on the meantime due to CO2 outgassing.

While adding smallish amounts of chlorine for daily maintenance, those pH fluctuations are quite small. But when adding larger amounts they can be more significant.

The pH change from about 7.7 to about 8.2 is consistent with an FC increase of about 7ppm with a TA of 80.

 

[TheMauiBeach]

I didn't know what to do about the pH reading of 8.19 being the highest I had ever seen and was only 12 hours after it was 7.66. I was following the recommendation to get my FC level quite a ways up from the 3.5-4 range to 8-10 due to CYA levels. I thought that meant that I need to maintain that FC level as much as possible. I am going to add liquid chlorine to keep it around FC of 8 throughout the day today. Does that mean that any chlorine effects on pH would keep occurring as anything that burned off would be replaced by chlorine I add to keep that higher FC level? I just checked pH with the drop test and it is down to the 7.6 range. That puts my CSI at -.08 right now, roughly. Thanks for the help.

 

[proavia]

Please post your test results vertically. They are way to hard to read horizontally or within the body of your message.

FC
CC
pH
TA
CH
CYA
Water temperature
CYA

Alternately, use PoolMath and link to your forum account. Your results logged in PoolMath will then show when someone clicks on your profile icon and then PoolMath Logs.

Add your pH meter info to your signature.

 

[mgtfp]

I didn't know what to do about the pH reading of 8.19 being the highest I had ever seen and was only 12 hours after it was 7.66. I was following the recommendation to get my FC level quite a ways up from the 3.5-4 range to 8-10 due to CYA levels. I thought that meant that I need to maintain that FC level as much as possible. I am going to add liquid chlorine to keep it around FC of 8 throughout the day today. Does that mean that any chlorine effects on pH would keep occurring as anything that burned off would be replaced by chlorine I add to keep that higher FC level? I just checked pH with the drop test and it is down to the 7.6 range. That puts my CSI at -.08 right now, roughly. Thanks for the help.

The effect on pH is noticeable when adding larger amounts of chlorine, which is why the SLAM guideline asks to reduce pH before starting the SLAM. When adding smaller daily maintenance doses it should be small enough to not worry about.

Are you using PoolMath to calculate CSI?

 

[TheMauiBeach]

Yes, using PoolMath for CSI.
pH 7.6
TA 80
CH 210
CYA 70
91F
CSI -.08

I said "roughly" above, because of the pH method I used as a check, and as I expected the TA might come down some from the MA I added.
I checked the pH with the meter a few minutes ago, and it is 7.61 now. The good news is that it was 7.59 at 11am, so it hasn't risen much over the last 5+ hours.

I'll do the full set of tests closer to dark and add chlorine and MA as needed.

 

[SoDel]

Thanks for the help.

I added 79 oz of 12.5% chlorine at night, on 8/15. On 8/16 in the evening FC was down to 4.0, so I added another 40 ounces. It sounds like I need to go way over the target, so it never goes below 8-10. I was using the suggested 7.5% of CYA as my target while I figure out how much to add each night. 7.5% is FC of 5.25. I thought I needed to mostly stay over that number. It should be well over that all night and into the day. I haven't had any algae yet... knock on wood. I was planning another partial water change out, to get the CYA down further, but will wait on that to conserve water since it has been SOOO hot here in Houston.

I will check my fill water and post a record of that.

My main concern is with the TA going so low, my carbonate alkalinity will be super low, so is that "bad" for the Pebble Tech surface? Does it matter since it is a new surface?

As an opinion (and we all have them lol) 7.5% FC of CYA is a minimum (and imho, bare minimum), not target. You do seem to indicate you are using that as a floor . Prioritize sanitation, then CSI balance. It does no harm to “run hot” a bit on chlorine and the additional cost is minimal. May I humbly suggest 10% of CYA as an FC floor? Algae bloom will cost far more. It has been a while so I’ve mostly forgotten the contact time effect of the ratio on the “bad” pathogens — not much of a factor, at least in my pool (mostly just one bather and it’s not me lol).

 

[mgtfp]

Your CSI looks a bit higher than I calculate. Are you entering a salt value of 0? I would expect a value closer to -0.2 with above parameters. At pH 8.1, CSI should still be below 0.3, and even a short time at pH 8.2 should not cause problems. I wouldn't worry about it too much.

In a liquid chlorine pool where usually no salt measurements are taken (and salt tracking turned off in PoolMath), PoolMath assumes a default salt level of 1000pm. This is because chlorine doesn't actually leave the pool when it is spent, but turns into chloride (salt). And adding muriatic acid also adds some chloride over time.

Many liquid chlorine pool owners have found salt levels around 1000ppm in their pools when taking a salt measurement before adding more salt when changing over to an SWG.

 

[TheMauiBeach]

That is interesting. I haven't entered a salt or borate value. They both show 0. I typed in 0 and hit enter and just checked the CSI again. I get -.08 with the last parameters in post #14.

pH 7.6
TA 80
CH 210
CYA 70
91F
CSI -.08

If I change the pH to 8.1, the CSI is +.40.

If I type 1000 in the Salt field, I do get a CSI of -.18 with pH 7.6, and a CSI of +.3 with pH of 8.1, to compare to what you stated above. But, it has always shown 0 when I use it. I use the online version.

Is the "salt" field for TDS? The pool store samples I had taken in showed mostly TDS values of 800. They were never higher, and occasionally a little lower. If so, I will start entering 800 if that is the correct way to have PoolMath calculate CSI. With 800 entered for "salt", I get a CSI of +.32 with a pH of 8.1, and -.16 with a pH of 7.6. Thanks for catching that if my interpretation of what you are pointing out is correct.

 

[mknauss]

If you select Track Salt in Settings, it uses the value you enter for CSI. If you deSelect Track Salt, it uses 1000 ppm for calculations.

Your water does not have 0 salt. At a minimum, it has ~200 ppm if no form of chlorine or acid has been added.

TDS is more than 'salt'. It is all the chlorides, cya, calcium, etc.

 

[TheMauiBeach]

I should use 200 in the salt field? 1000?

Thanks.

 

[mknauss]

Unless this pool has a SWCG, turn OFF Track Salt.