Does Soda Ash expire?

[Klutz14159]

My CYA has dropped to zero over the winter due to a leak + water replacement. Was about to dump in some CYA stabilizer until I noticed how drastically it drops pH.

I found an ancient bag of Leslie's Soda Ash in the pool shed where the bag is just about to crack apart into brittle flakes, but inside is a nice white crystal powder. Is this still usable or should I buy a new bag to raise the pH back up? My TA is somehow still around 90 even though CYA and Calcium have been dropping all winter long.

 

[newdude]

It's good forever, and doesn't break down into anything else.

 

[JoyfulNoise]

CYA is a relatively weak acid. You shouldn’t really see much, if any, drop in pH (perhaps 0.2 or so). I doubt you’ll need the soda ash.

When you have a leak, your chemical levels revert to whatever your fill water values are. Since there is no CYA in fill water, that will slowly trend to zero as pool water leaks out and fresh water takes its place. Most fill water has carbonate alkalinity in it so your pool water TA will always trend towards whatever the fill water value is, not zero. Same is true for CH.

 

[Klutz14159]

CYA is a relatively weak acid. You shouldn’t really see much, if any, drop in pH (perhaps 0.2 or so). I doubt you’ll need the soda ash.

When you have a leak, your chemical levels revert to whatever your fill water values are. Since there is no CYA in fill water, that will slowly trend to zero as pool water leaks out and fresh water takes its place. Most fill water has carbonate alkalinity in it so your pool water TA will always trend towards whatever the fill water value is, not zero. Same is true for CH.

Poolmath calculator predicted pH drop of 0.55 for 30ppm CYA rise. Plugged new pH back into calculator and it sent my CSI to -0.68, so going to split it into several rounds of treatment and check each round against expectations and keep pH levels up. Just raised my CH to 200 and going to start using Cal-hypo for chlorination since it's now cheaper than liquid chlorine, and a whole lot more stable so I can hoard enough to get through the summer months.

This is a really old pool so already developing some bald spots of gunite all around. Waiting for some non-drought year in California to replaster, as if that might ever happen again...

Thanks for the reminder about checking fill water. I had checked fill water CH 4 years ago when I first started reading TFP but didn't check TA. I should probably recheck them anyway since water sources have changed over the years with closure of our biggest nearby reservoir for earthquake retrofits.

 

[JoyfulNoise]

PoolMath pH calculations are not accurate with large additions of any chemical. They typically can't predict more than a 0.2 drop or increase in pH accurately. I have added many, many pounds of CYA and it has almost no effect on pH. It dissolves very slowly and the alkalinity of the pool water is more than enough to buffer the change in pH. Keep the soda ash on hand if you like but I sincerely doubt you will need any of it. Plus, you really don't want to add soda ash to a pool - it raises pH and TA very quickly and can lead to cloudiness as it will cause calcium to scale. If you were concerned about pH or felt it was a little too low, you could just as easily add baking soda to the pool which raises the alkalinity immediately but only slowly increases pH. Your plaster is not going to be damaged by minor excursion in pH ... it's old and worn out from years of use, adding a little bit of CYA to the water is not going to do anymore damage than what is already there...

 

[Klutz14159]

Been using trichlor pucks like crazy last two months trying to get CYA raised up the easy way before solar cover goes in for swim season and I have to switch back to liquid chlorine.

Happy to report that my ancient bag of soda ash raised pH back up exactly as poolmath predicted! Just have to fish all these flakes of disintegrated plastic bag out of the pool now.