Can TA be too low?
- Thread starter DLSDO
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60 is about as low as you should go with TA, maybe 50 in a few cases. TA helps keep the PH from fluctuating wildly. If you were using trichlor this would be a fix right this moment kind of thing, but since you are using bleach it isn't a big deal. Raise the TA a little, to between 70 and 90, when you have time.
Thanks Jason. So either a high or low TA results in wild fluctuations in pH. Makes sense.
Yes, but for two different reasons. Very low TA means no buffering of PH, so even some blown in dust is enough to change the PH. Very high TA means lots of CO2 outgassing from only a little aeration, which raises PH.
Interrupt in thread. I apologize.
So, does this mean if my PH always rises my TA can not be too low ?
Below 70 now with SWG and starting to think about it.
You also need TA, specifically the carbonate component of TA (so subtract one-third of the CYA level from TA) to saturate the water with calcium carbonate to prevent pitting of pool plaster. The Pool Calculator does this calculation for you including the adjustment to TA for CYA.
You will notice that the higher salt levels create a more corrosive saturation index. At a pH of 7.5, TA of 70 ppm, CYA of 80 ppm, CH of 300 ppm, TDS of 3200 ppm (for salt level near 3000 ppm), temp of 85F, this results in a saturation index of almost -0.5. So in this scenario, it would be better to keep the pH closer to 7.7 to 7.8 which would also help slow down the rate of rise in pH (lower TA and higher pH slow down this rate) and would have an index of -0.3 to -0.2 which is fine in an SWG pool.
The above isn't a huge deal, but if you keep pushing it and lower TA to 50 ppm, then at a pH of 7.5 the index is down below -0.7. This is why I generally give a lower limit for TA of 70-80 ppm in an SWG pool when the CYA is 60-80 ppm. In a non-SWG pool with lower salt and CYA levels, one can go as low as a TA of 50 ppm if they target a pH of 7.7 though this is a pretty extreme scenario and most are fine at 70-80 ppm TA with 7.5 or so pH. Again, in both situations, this assumes that the tendency is for the pH to rise; in a pool using an acidic source of chlorine such as Trichlor, the TA should be much higher such as 100-140 ppm to provide sufficient buffering against the strong acidity.
If you still find the pH to be rising more than you'd like at the lower TA level of 70 ppm and at a higher pH level of 7.7, then you might consider adding Borates to the pool as described here. Not everyone finds borates to help with rising pH, but many do.
Richard
You will notice that the higher salt levels create a more corrosive saturation index. At a pH of 7.5, TA of 70 ppm, CYA of 80 ppm, CH of 300 ppm, TDS of 3200 ppm (for salt level near 3000 ppm), temp of 85F, this results in a saturation index of almost -0.5. So in this scenario, it would be better to keep the pH closer to 7.7 to 7.8 which would also help slow down the rate of rise in pH (lower TA and higher pH slow down this rate) and would have an index of -0.3 to -0.2 which is fine in an SWG pool.
The above isn't a huge deal, but if you keep pushing it and lower TA to 50 ppm, then at a pH of 7.5 the index is down below -0.7. This is why I generally give a lower limit for TA of 70-80 ppm in an SWG pool when the CYA is 60-80 ppm. In a non-SWG pool with lower salt and CYA levels, one can go as low as a TA of 50 ppm if they target a pH of 7.7 though this is a pretty extreme scenario and most are fine at 70-80 ppm TA with 7.5 or so pH. Again, in both situations, this assumes that the tendency is for the pH to rise; in a pool using an acidic source of chlorine such as Trichlor, the TA should be much higher such as 100-140 ppm to provide sufficient buffering against the strong acidity.
If you still find the pH to be rising more than you'd like at the lower TA level of 70 ppm and at a higher pH level of 7.7, then you might consider adding Borates to the pool as described here. Not everyone finds borates to help with rising pH, but many do.
Richard
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