Lower PH @ closing to compensate for upward drift?

[marmo]

I'm not sure if this is the correct section so mods please feel free to move it.

I have a 1 year old gunite built in. Last year we closed the pool at a balance 7.5 ph. This year when we opened it the PH was 10 and crystal formation formed on the entire gunite surface. It felt very sharp on the feet. At any rate I lowered the PH to approx 6.8 and after a week plus brushing things returned to normal. I understand this PH drift happens with newer plaster pools and it should calm down over time, however, I want to avoid this problem next year. So I was thinking to power the PH down low to compensate the natural drift upward. And that is my question, how low can you go safely at closing to avoid this problem? Thanks in advance.

 

[Texas Splash]

Others will probably have additional comments, but I'll start-off the replies by saying that your experience last year may have been contributable in-part due to the (new) curing plaster. I would be cautious about going too low because of your heater, unless you purge or by-pass it upon closing. You may have additional equipment that can't handle a pH too low. Not to mention your plaster, at which point too low and it starts to leach as well. I would hope that the majority of pH increase from the new plaster has passed, and once the SWG is turned-off at closing (aeration), your pH should be much more stable.

Another important factor is your TA. What is it right now? If it's fairly high, it will pull the pH up with it. You may want to post that number for us so we can advise you.

My input would be a closing pH of 7.2. No lower than 7.0. By the way, can you please update your location for us? It helps when we're reviewing. Thanks.

 

[chem geek]

I agree with the 7.2 and no lower than 7.0 pH, but note that carbon dioxide outgassing is faster at lower pH so your pH won't stay low for very long unless the water is colder or you have a pool cover (solid, not one with holes to let rain fall through).

 

[marmo]

Thanks gentlemen. I'm in Northern New Jersey, I'll update profile. Also my TA has been approx 90 steady all season. I use a Solid cover with no drain and pump water off.

 

[Texas Splash]

You're very welcome. Please note that if you would like, you can indeed go a bit lower with your TA which should help keep your pH from climbing as fast. TFP has adjusted the Recommended Levels chart, so you have some wiggle-room if you want to lower your TA down to 60 or 70. Just a thought. Good luck on your closing, and have a great day.