Naturally rising pH?

EnormCrane

Member
Mar 29, 2019
6
Modesto
Hey all. I have a pebbletec, 27k gallon pool, cartridge filter. When I moved in in February, it was my first pool, and a friend of mine who works in the pool industry recommended and helped me install an inline tab feeder. After following this website for a few months, I decided eleven days ago to switch off the feeder and go the BBB route. It just makes more sense than draining and refilling once a year.

On to the question: my pool likes to sit at about 7.6-7.8 pH. I've added soda ash to keep it there twice since moving in. Now that I've switched (not blaming the method, just timeline) my pool is increasing in pH. Three days ago, it measured at 8.1. I added 32.6 oz of muriatic acid (as per the pool math recommendation, and in smaller doses over time, testing often). That brought it down to 7.4 two days ago. Today, it measured at 8. From what I've read, there must be some other variable that's doing this, but I can't figure it out. The weather has heated up significantly the last couple weeks, but I can't imagine that would be it.

Some information about me as a person. When I latch onto something, I obsess. I decided that I would be the pool guy when we moved in, and have been laughed at by friends and family for how often I'm testing, adjusting, talking about, researching, and maintaining my pool. The water has ALWAYS been crystal clear.

Here are the rest of my readings from today:

FC: 6.8 (high, but my CYA demands it... stupid pucks)
CC: 0.4 (has been mostly at 0 until about 22 hours ago)
TA: 90 (high side of the acceptable range... is this part of the problem)
CYA: 75 (It was 80 when I switched. I've been deliberately splashing a lot)
pH: 8.0
CH: 280
temp: 84 (I live in central valley of CA, where it's 109 this week most days)
CSI: .34

Side note: I'm leaving on a four day vacation, and I lose about 3 ppm FC per day, so I'm going to bring levels up to 15 tonight so that it's hopefully at about 9 when I return on Friday night.

Please advise. Can't wrap my head around this one.

Thanks, guys.

Zach Stillman
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
9,850
Northern NJ
Trichlor tablets contain acid in addition to chlorine and CYA. The tablets have been keeping your pH down. Now you are seeing the natural pH rise.

Needing to lower pH in a plaster pool every 3 to 4 days is normal. The lower you take your pH the quicker it will rise. You need to manage your CSI. CSI of +0.34 long term puts you at risk for scale.

You need to lower your TA to 60 and then a pH of 7.8 will give you a negative CSI. That should give you a more stable pH. Read ...


What is the pH and TA of your fill water?

Do you have a spillover or water features running? How old is your plaster?

Your CYA is 80. If the dot disappears between 80 and 70 we round up and call it 80. You can't estimate where CYA 75 is between the lines since the scale is logarithmic, not linear.

With a CYA of 80 your target FC should be 9-11. FC/CYA Chart FC of 6.8 is close to your minimum.

CL loss is not linear as you raise your FC above the targets. I think you will have low FC at the end of 4 days starting with FC of 15.
 
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EnormCrane

Member
Mar 29, 2019
6
Modesto
Thanks for the heads up about needing to lower pH and that being normal. To answer your questions:

No spill over features. My returns are pointed up, so that contributes to aeration.

I will drop the TA. Thanks for that.

Never have measured my fill water. I’ll do that when I get back, along with lowering TA. What a newb! That seems so basic. Bummed I missed it.

Yes. My target is FC is 9. It was at 9 this morning. I measure at the end of the day, so that makes sense.

I’ll bite: where should I get to before leaving if 18 is going to be low (btw, I meant to write 18, which is what I added for tonight, but it will still be low if loss isn’t linear.)
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
9,850
Northern NJ
Just added acid to lower pH to 7.2. Hopefully 4 days of jets running 8 hrs a day is enough aeration to bring it back up to swimable by Friday.
Pool is swimable with ph anywhere in the 7s.

I would not aerate for 4 days while away. Your pH can rise naturally from 7.2 to 8 in 4 days.
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
9,850
Northern NJ
Yes. My target is FC is 9. It was at 9 this morning. I measure at the end of the day, so that makes sense.
Better to target the high end of the range at 11 so your FC does not drop so close to minimum.

I’ll bite: where should I get to before leaving if 18 is going to be low (btw, I meant to write 18, which is what I added for tonight, but it will still be low if loss isn’t linear.)
Well you are stuck. Vacation is when we suggest using tablets if you can take a bit more CYA.

Which would you possibly rather do when you return from vacation...

1) Drain some water to lower CYA from the tablets used? Or,

2) perform the SLAM Process to get rid of algae because your FC dropped too low during your vacation?