My pH went down very confused

[Davegnh]

Hopefully some of the chemistry gurus can help me here. I have a 2-year-old pool it's been very consistent for the last 2 years. I've had to add about 16 oz of muriatic acid every three days. I've never had the pH go down. I opened the pool a couple weeks ago pH was high added 16 oz of muriatic acid to get pH down to 7.2. it slowly drifted up to 7.8 two days ago. Today pH measured 7.2..... I've never had my pH go down. At the same time my chlorine sank from 7 to .5 with no CC's. The temperature of the water has been high 50s to low 60s. But today it took it up to 67 as the air temperature was low '80s. Water looks perfectly clear. I'm scratching my head on what might be going on thinking ammonia as I did add a pound of 65% Cal hypo after low chlorine reading and about an hour later my chlorine was 3.5 (should have been 7.5). I'm using Cal hypo because I like to increase my calcium level to 450+ to make my CSI happier.

Fc 3.5
Cc 0
Ph7.2
Ta 50
Ch350
Cya 70
Salt 3150
Temp 67
CSI -1.12

 

[Davegnh]

Forgot to mention I have my saltwater chlorine generator set to 20% which is about three PPM a day which generally this time of year should increase the amount of chlorine in my pool.

On the plus side today was my first swim of the year my son challenged me to go swimming in 67° water. Challenge completed.

 

[HermanTX]

I open the pool a couple weeks ago pH was high added 16 oz of muriatic acid to get pH down to 7.2. it slowly drifted up to 7.8 two days ago. Today and measured 7.2..... I've never had my pH go down. At the same time my chlorine sank from 7 to .5 with no CC's. The temperature of the water has been high 50s to low 60s

I was going to ask how many hours per day is the pump running, until your updated post with SWCG running. I was thinking your pool may still be mixing with the heavier water on bottom.
Let’s not jump to ammonia as that creates a whole host of issues. Anyway - FC would disappear within an hour which yours is not.
Maybe add the time of day that you are testing so we can determine rate of decline.
Have you done an
Overnight Chlorine Loss Test. That would be the next step.

 

[Davegnh]

I just added another pound of Cal hypo 65% as a precaution.

I run the pump 24 hours a day at a very low speed.

I test in late afternoon 5:30 to 6:00 p.m..

I haven't done in overnight chlorine loss test as this was the first day I noticed the discrepancy. The thing that really was weird decline in pH as I've never seen that in my pool.

 

[Mdragger88]

Definitely do an
Overnight Chlorine Loss Test.

 

[Davegnh]

I'll do the overnight chlorine loss test. But what could have caused the loss of pH? I don't think I can have algae as my water temperature has been below 60 last couple weeks and just barely warmed above 60 in the last few days.

 

[ajw22]

How do you measure pH?

 

[Davegnh]

I use Taylor 2006c

 

[HermanTX]

I'll do the overnight chlorine loss test. But what could have caused the loss of pH? I don't think I can have algae as my water temperature has been below 60 last couple weeks and just barely warmed above 60 in the last few days.

Algae does not affect pH reading. Is your pH reagent still good within its expiration date?
pH can decline with additions of MA or stabilizer (CYA) - this could be a red herring right now. Let’s address the FC loss. Post the results ofOvernight Chlorine Loss Test

 

[ajw22]

I would not worry about a one time occurrence.

Monitor your pH and see what happens.

What is your TA?

 

[Davegnh]

After adding another pound of 65% Cal hypo 30 minutes ago free chlorine went up to 7. I'll check again before the sun comes up erg that means 5:00 a.m. chemicals are within date.

 

[HermanTX]

After adding another pound of 65% Cal hypo 30 minutes ago free chlorine went up to 7. I'll check again before the sun comes up erg that means 5:00 a.m. chemicals are within date.

Thanks. Is the SWCG off?

 

[Davegnh]

Yes chlorine generator is off

 

[Davegnh]

I would not worry about a one time occurrence.

Monitor your pH and see what happens.

What is your TA?

TA is 50 I've been trying to keep lower side. Because historically I've had so much acid to keep my pH in range.

 

[Davegnh]

So my free chlorine went up overnight to 10.5. I can only guess that the ccal hypo wasn't fully dissolved. I usually mix it in a 5 gallon bucket and dump it in. But the last pound I put in was being lazy and just sprinkled it around the pool. So looks like need to test again tonight.

 

[Davegnh]

I passed the overnight test with no change in Clorine test. Still baffled by the drop in PH. On the safe side think will get new regents for PH.

 

[Davegnh]

Now pH 7.6 does it take plaster 2+ years to settle down?

 

[ajw22]

Now pH 7.6 does it take plaster 2+ years to settle down?

Some plaster pools can never keep a stable pH.

 

[Davegnh]

Mine has always risen until this year. Baffled me