Hello all! 
I am in Naples, FL with a 5-year-old plaster pool that came with the purchase of our home. The pool has a SWCG and spillover spa – so the equipment is shared and the water maintained as “pool” until you turn on “spa mode,” which isolates the spa and only circulates water to the spa until pool mode is restored. The pool also has an “auto fill” for maintenance of a minimum water level (for skimmer function) when water is lost to evaporation. In the winter this can mean a fair bit of fill water as that is the dry season in Southwest Florida. Much less top-off water is needed in the summer due to heavy, frequent rains.
Current Values: (Measured with Taylor FAS-DPD Kit K-2006 + SALT kit) 10/9/2021
Temp 85 F
pH 7.8
TC 3.6 ppm
CC 0
CYA 70 ppm
Borates 36 ppm (measured using the drop titration method with bromothymol blue and mannitol)
TA 70 ppm (when corrected for CYA and Borates, Carbonate Alk is about 40)
CH 250
I have been maintaining a pool for about 11 years, but previously it was vinyl lined and in the Mid-Atlantic. My biggest challenge with this pool has been the constant upward pH drift (Henry’s law + SWCG + spillover, etc), which is exacerbated by the high carbonate alkalinity in our source water – about 300-330 ppm. (This water has been softened already so it has negligible CH – but softening has no effect on Alk.) It is a never-ending trek with the MA, and If I miss some time then scaling can become a real problem! The spa feature also means I have to be sure that my water conditions at any given time will still be balanced if the spa is used – suddenly increasing the temp to 102! I have worked diligently this year and seem to have everything under control, but I am noodling anything that I could do to make this easier.
So, I have two (potentially crazy) ideas and I would love to hear your reactions to them!
1) Would I get a benefit from installing a reverse osmosis system for the pool auto fill? The unit I am considering would remove 90% of the Alk, so my fill water would go from about 300 ppm to about 30. I know that this would also significantly lower the pH of the top-off water, making it unsuitable for a large drain and fill operation even if the unit had the capacity, but I think it will be fine for evap. make-up, especially since I am constantly adding MA as it is!?
My calculations (based on a year’s archived weather data) is that our worst-case daily evap. is about 0.25.” Which works out to about 70-75 gal per day. Most of the time it would be half that, maybe less. The system I am considering is rated to produce up to 300 gallon per day and the RO filter is expected to last 2-3 years. Since I need 75 gal per day or less, I think I would get a reasonable service period out of a set of filters/membranes. I would use any pre-filters that are recommended to protect the membrane – but not any post filters since the water isn’t for potable use.
2) Would it be crazy to shoot for an actual carbonate alkalinity of 30 ppm, while still maintaining borates (probably at 50 ppm)? What would be the potential dangers?
I am aware that carbonate alkalinity buffers against acidification of the water, but this is LITERALLY never a problem in my pool. If the carbonate alkalinity were 30 ppm, at 80 degrees F, Henry’s law demands (predicts?) an equilibrium pH of 7.9. If I raised my CH to about 300 (or higher?), the water would be near perfectly balanced at 7.9 and, theoretically not keep rising because we’ve reached equilibrium with the air, right? I keep thinking that the only time I ever had low pH in any pool I have maintained was up in the Mid-Atlantic when opening in the spring. This part of the pool life cycle doesn’t apply to my current pool which is open and maintained year-round. My current pool never has a pH drop of any size unless I add acid – there is no fluctuation, only rise. And I basically already maintain my pool at 7.9 (7.8-8.0) because that’s where it “wants to be.” Would lowering the carbonate alk to 30 ppm make this less of a fight?
I have traditionally used the Taylor Watergram, but just found your Pool Math app and I’m giving it a try. I’m not sure how to feel about the CSI numbers produced by the app versus the Taylor Watergram numbers. Pool Math says the above scheme (pH 7.9, TA 70, Borates 50, CH 300, CYA 70, and salt 4000) would yield a CSI of -0.22, Watergram yields +0.05. I think Pool Math accounts for TDS (salt) where Watergram does not, because if I input 0 for salt Pool Math give me +0.04. Is it really acceptable to keep a plaster pool at a CSI of -0.22? The app says its good, but I don’t want to dissolve my plaster over time. Although I guess I have been all along since the Watergram just wasn't accounting for the TDS ...
I would really appreciate any thoughts your knowledgeable membership has on these ideas. Thanks!
10500 gal plaster pool with Spa and spillover, PureChlor SWCG, Jandy CS200 Cartridge Filter, Pentair IntelliFlo VSF pump, Intertek 6350 Pool and Spa Heater and iaqualink system for lights.
I am in Naples, FL with a 5-year-old plaster pool that came with the purchase of our home. The pool has a SWCG and spillover spa – so the equipment is shared and the water maintained as “pool” until you turn on “spa mode,” which isolates the spa and only circulates water to the spa until pool mode is restored. The pool also has an “auto fill” for maintenance of a minimum water level (for skimmer function) when water is lost to evaporation. In the winter this can mean a fair bit of fill water as that is the dry season in Southwest Florida. Much less top-off water is needed in the summer due to heavy, frequent rains.
Current Values: (Measured with Taylor FAS-DPD Kit K-2006 + SALT kit) 10/9/2021
Temp 85 F
pH 7.8
TC 3.6 ppm
CC 0
CYA 70 ppm
Borates 36 ppm (measured using the drop titration method with bromothymol blue and mannitol)
TA 70 ppm (when corrected for CYA and Borates, Carbonate Alk is about 40)
CH 250
I have been maintaining a pool for about 11 years, but previously it was vinyl lined and in the Mid-Atlantic. My biggest challenge with this pool has been the constant upward pH drift (Henry’s law + SWCG + spillover, etc), which is exacerbated by the high carbonate alkalinity in our source water – about 300-330 ppm. (This water has been softened already so it has negligible CH – but softening has no effect on Alk.) It is a never-ending trek with the MA, and If I miss some time then scaling can become a real problem! The spa feature also means I have to be sure that my water conditions at any given time will still be balanced if the spa is used – suddenly increasing the temp to 102! I have worked diligently this year and seem to have everything under control, but I am noodling anything that I could do to make this easier.
So, I have two (potentially crazy) ideas and I would love to hear your reactions to them!
1) Would I get a benefit from installing a reverse osmosis system for the pool auto fill? The unit I am considering would remove 90% of the Alk, so my fill water would go from about 300 ppm to about 30. I know that this would also significantly lower the pH of the top-off water, making it unsuitable for a large drain and fill operation even if the unit had the capacity, but I think it will be fine for evap. make-up, especially since I am constantly adding MA as it is!?
My calculations (based on a year’s archived weather data) is that our worst-case daily evap. is about 0.25.” Which works out to about 70-75 gal per day. Most of the time it would be half that, maybe less. The system I am considering is rated to produce up to 300 gallon per day and the RO filter is expected to last 2-3 years. Since I need 75 gal per day or less, I think I would get a reasonable service period out of a set of filters/membranes. I would use any pre-filters that are recommended to protect the membrane – but not any post filters since the water isn’t for potable use.
2) Would it be crazy to shoot for an actual carbonate alkalinity of 30 ppm, while still maintaining borates (probably at 50 ppm)? What would be the potential dangers?
I am aware that carbonate alkalinity buffers against acidification of the water, but this is LITERALLY never a problem in my pool. If the carbonate alkalinity were 30 ppm, at 80 degrees F, Henry’s law demands (predicts?) an equilibrium pH of 7.9. If I raised my CH to about 300 (or higher?), the water would be near perfectly balanced at 7.9 and, theoretically not keep rising because we’ve reached equilibrium with the air, right? I keep thinking that the only time I ever had low pH in any pool I have maintained was up in the Mid-Atlantic when opening in the spring. This part of the pool life cycle doesn’t apply to my current pool which is open and maintained year-round. My current pool never has a pH drop of any size unless I add acid – there is no fluctuation, only rise. And I basically already maintain my pool at 7.9 (7.8-8.0) because that’s where it “wants to be.” Would lowering the carbonate alk to 30 ppm make this less of a fight?
I have traditionally used the Taylor Watergram, but just found your Pool Math app and I’m giving it a try. I’m not sure how to feel about the CSI numbers produced by the app versus the Taylor Watergram numbers. Pool Math says the above scheme (pH 7.9, TA 70, Borates 50, CH 300, CYA 70, and salt 4000) would yield a CSI of -0.22, Watergram yields +0.05. I think Pool Math accounts for TDS (salt) where Watergram does not, because if I input 0 for salt Pool Math give me +0.04. Is it really acceptable to keep a plaster pool at a CSI of -0.22? The app says its good, but I don’t want to dissolve my plaster over time. Although I guess I have been all along since the Watergram just wasn't accounting for the TDS ...
I would really appreciate any thoughts your knowledgeable membership has on these ideas. Thanks!
10500 gal plaster pool with Spa and spillover, PureChlor SWCG, Jandy CS200 Cartridge Filter, Pentair IntelliFlo VSF pump, Intertek 6350 Pool and Spa Heater and iaqualink system for lights.
