How many days can I let pH stay out of recommended before issues?

[gilbee]

I'm going out of town for 5 days, and I'm leaving the pool care in the hands of my lovely wife. The last time I did this, I came home to a pool with very low chlorine levels (.5 or 1) and one of the skimmer weirs blocked causing air to be introduced into the pump. No bueno. Since that event, I've realized that she isn't going to stay on top of monitoring things, so I need to make the pool as much autopilot as I can when I'm out. I bought a SWG so chlorine wouldn't be an issue, but since my plaster is still curing (along with a spa overflow and now the swg bubbles), I normally add acid daily to keep the pH in check. Because the SWG is so new (installed July 4) and I'm still playing with the settings and pump run times on it...I didn't want to take any chances of the FC dipping, so I added 1 gallon of 10% LC this morning. This will raise the chlorine above 10ppm, which will make pH tests ineffective until it comes back down.

My question---how many days can a plaster pool have a pH above 8.2 before scaling starts to occur? Based on my reading and addition history, I have been adding anywhere from 8 to 32oz of acid per day to keep the pH in check. I'm inclined to try to get her to add 4-8oz per day just to stave off extremely high numbers without overshooting, but I hate just guessing at something like adding acid for pH...

What say you?

 

[elwood58]

This is a tough one without seeing a full set of test numbers. Your CH numbers will say a lot about the probability of scaling occurring. With a new finish, you have to be more concerned with leaching calcium from your finish, which is not good. I would be tempted, provided your CH is above 250, to manage pH to a lower number while you are away. I would shoot for a target of 7.4. That way, if she forgets a dose or two, you will not get too high.

Increasing the % output on your SWG is not going to hurt things either.

 

[Richard320]

You might want to try this approach: 2 week vacation - I trust nobody to take care of the pool!!

 

[JoyfulNoise]

You said your plaster is still curing. How new is your plaster?

 

[gilbee]

This is a tough one without seeing a full set of test numbers. ...

My most recent full test (I only test Chlorine and pH during the week, with a full test at the end of each week) is as follows:

FC 5
CC 0
TC 5
pH 8.2
TA 70
CH 275
CYA 60-70
salt 3400

After this test obviously I added acid to lower the pH back down...

Increasing the % output on your SWG is not going to hurt things either.

Yup, did that too.

- - - Updated - - -

You said your plaster is still curing. How new is your plaster?

Plaster was finished and water went back in early June...June 9 I believe. When I say still curing, I mean that for the foreseeable future (1 year I've read here), the plaster will be causing the water to continually rise the pH more than after that point.

 

[chyvan]

If it helps any, I got new plaster 3/7. I was using 1 quart of acid every 3 to 4 days. That went on until 5/15. Now, I'm down to about 1 quart per week.

For the leeching, I thought that required low pH and low CH. For that reason, I was letting my pH run around 7.6 to 7.8 because I thought I was doing my plaster a favor. Is that wrong, or did you just tell him to go low knowing it was going to rise just because it's new plaster?

 

[gilbee]

For that reason, I was letting my pH run around 7.6 to 7.8 because I thought I was doing my plaster a favor. Is that wrong, or did you just tell him to go low knowing it was going to rise just because it's new plaster?

You were keeping it right, and when I'm home every day, that's more or less where I target for (sometimes I target for 7.4 or 7.5, but generally the target is 7.6-7.7, simply because I know if I drop to 7.4-7.5, it will be 7.8 by the afternoon), but I know if I leave the pool for more than a day or two without adding any acid, I will come back to an 8+ pool.