Do TA constituents matter?

[Saturn94]

Some background…

Our pool has a habit of pH dropping significantly over the winter while closed (solid tarp cover), usually Oct to May. I’ve seen it drop as much as 7.6 to about 6.8 over the winter. At opening, I usually have to add a couple boxes (65 oz box) or so of borax to raise pH about where I want it, about 7.5. Once there, it’s usually pretty stable throughout the swim season. Once in a great while, I may have to add a little borax during the season.

TA is usually about 50ppm at opening. After adding CYA, borax, and boric acid, TA usually bumps up to 70-80ppm. As I understand it, borates (and CYA?) contribute to the TA number, hence the increase. Please correct me if my understanding is wrong.

Many, many years ago, before I learned about the pool care methods taught here, I use to add bicarb to get TA up to standard industry recommended levels. Of course that resulted in needing regular additions of acid to combat pH rise. Since learning about the methods taught here (actually on the original Pool Forum many years ago), I stopped adding bicarb and let TA drop. I haven’t added bicarb since.

Which brings me to my question. Do the constituents of TA matter as long as the total number is within range? Is it possible that the lack of bicarb additions cause, or contribute to, the pH drop I observe over the winter? Should I be adding bicarb in the spring to bring TA up to my target (60-80)? Or is it fine to just continue to add borax each spring to raise pH and not worry about the pH drop over the winter while closed?

 

[JamesW]

They matter for the CSI and for determining the effect on pH rise due to carbon dioxide outgassing.

 

[Saturn94]

They matter for the CSI and for determining the effect on pH rise due to carbon dioxide outgassing.

Any thoughts on whether or not I should be adding bicarb in my situation, ie stable pH during the swim season, falling pH over the winter when covered/closed?

 

[Newdude]

If you had a mesh cover i'd expect those drops from the rain mixing. Seing how 'solid' tarps are really a mesh, i'd blame that. Maybe a high quality waterproof tarp stays that way for a while, but never for long IMO.

Another experiment would be to close on the high side of both ranges and see if it still dropped, or dropped as much. Low Ph (really low) wrecks liners so i'd rather be proactive than reactive here.

 

[Saturn94]

If you had a mesh cover i'd expect those drops from the rain mixing. Seing how 'solid' tarps are really a mesh, i'd blame that. Maybe a high quality waterproof tarp stays that way for a while, but never for long IMO.

Another experiment would be to close on the high side of both ranges and see if it still dropped, or dropped as much. Low Ph (really low) wrecks liners so i'd rather be proactive than reactive here.

I also suspect rain water seeping in through the cover may be contributing to pH drop. Although, if rain had that much impact, why don’t I see this issue during the swim season with much more rain getting in?

What would be considered “really low” pH? Do you have any specific recommendations or proactive steps to take; maybe raise pH (with borax?) and TA (with bicarb?) at closing? I don’t want to overdo it, however. It’s been nice not having to add acid for many, many years.

I suspect over the years pH hasn’t been dropping “really low” since the liner has lasted 21 years so far. Other than being completely faded, it’s still in good shape.

 

[Newdude]

Although, if rain had that much impact, why don’t I see this issue during the swim season with much more rain getting in?

Because during the season you get an inch or two tops before its well mixed. It may be 2 ft during the off season by you, and 3 ft further north.

What would be considered “really low” pH?

I don't believe there is an official threshold but 5s would wrinkle a liner. Maybe low 6s.

 

[AUSpool]

Have you ever tested for borates? Do you know what your tap water pH and TA is. When we run a low TA both CyA and borates start to share a greater portion of the total. But both CyA and borate alkalinity’s are a little different from carbonate alkalinity in that CyA and borate alkalinities are influenced by the pH while carbonate alkalinity influences the pH. It’s a subtle difference and complicated.

In winter, cover on, no evaporation, no tap water with TA, lots of rain that has a pH close to 7, and some oxidation of organics that tend to be acidic reactions. Everything is trending toward a lower pH but there would be a limit - generally at what ever your testing at opening.

Summer, cover off, higher evaporation, input of carbonate alkalinity from the tap water. After initial balancing your water is reaching a high pH equilibrium point then it has through winter but it not continuing to increase with the low TA.

If it helps you could add a little bicarb at closing. Maybe 10-20ppm. And or at a little to the mix at opening ~10ppm bicarb maybe.

Yes, the constituents of TA and concentrations matter. Formulations of lots of things depend on it. Things like eye drops, various medications, buffer solutions, skin and hair products, etc.