PH Drifing Up with low TA?

[JoeMX82]

Numbers first:

PH: 7.8
TA: 75
CYA: 90
CH: 300
FC 5.5
TC 5.5
No SWG ( I know CYA is high - on a bleach only diet) 30K in ground pebble tec built 2014

I bought this home four months ago and when I moved in PH and TA where both very low. Initially raised TA to ~100 and PH to 7.5 but from here I am constantly been fighting PH drifting up. The pool gets minimal use as I do not have kids and I do not run the water fall features to try to avoid PH drift. I do have an infinity edge spa that gently trickles over into the pool but not sure how much that would contribute to PH rise. I keep adding PH minus with the thought that perhaps when TA gets a bit lower the rise will stop but no change to date. I am now getting nervous to lower TA any further for the following reasons:

• One my TA of 75 is on the low end of most acceptable scales
• My adjusted TA would be closer to 45 due to my high CYA levels

Question is what should I do? Would raising TA help by chance? But then I think that higher TA causes PH drift which is exactly what I am fighting. However, lowering TA anymore seems it might start getting corrosive? Any advice is greatly appreciated.


Additionally I do not have PH bounce - I check PH each day and it consistently rises from 7.5 to 7.9 and up over about a week or less. I am using 8% bleach at about 3/5 a gallon a day. I test with the TF-100 FAS-DPD test kit.

 

[Cinic]

It's OK to go below TA of 70 if you keep an eye on the CSI. My pool's pH rise slows way down when I keep the TA in the 50-60 range. There are lots of examples of this throughout the forum.

 

[Jimrahbe]

Joe,

I agree with John... try lowering your TA to 60 and see how the pH responds. I would also use Muriatic Acid to lower TA vs pH minus.

Jim R.

 

[JoyfulNoise]

It's important to remember that the "aggressiveness" of your water towards plaster does not solely depend on TA. The Saturation Index of the water (whether LSI, CSI or Ryznar Index)
is based on multiple parameters - pH, TA, CH, TDS (from salt) and temperature. All of these parameters play a role in determining how your plaster will respond to the water in the pool.

This is why TFP Recommendations, unlike other venues, does not bother the user with knowing what the adjusted alkalinity because that number, in and of itself, tells you nothing about the aggressiveness.

 

[JoeMX82]

Really appreciate the responses! Would like to clarify my understanding on the comment quoted below. Essentially it is TA and not adjust alkalinity that is used in the SI, right?
If so, I am calculating my SI as follows:

Water temp of 67 = 0.5
CH 300 = 2.1
TA 75 = 1.9
PH = 7.8
Salt <1000 = 12.1
Thus SI = 0.2 --> Does that seem right? If so, I drop my PH to 7.5 and TA to 50 I will be at -0.2 which I can bring back by raising my CH?

If all of my above understanding is correct, I am just wanting to make sure that low TA will not by itself increase the risk of copper being dissolved from my heater, etc. Reason I ask is the previous owner made this error but it was combined with low PH and CH so it was a really bad deal. Just want to make sure as I am scared to do any damage here.

Thanks again for all the help!!

 

[JamesW]

Try keeping the ph at 7.8 to 7.9.

 

[JoyfulNoise]

If you use Pool Math, your CSI calculates out to roughly -0.15. That is water that is only slightly undersaturated with calcium relative to the equilibrium saturation point. Your water is fine. Lowering your TA to 60ppm would only decrease the CSI to -0.34 which is also just fine. We recommend that pool water be kept within the bounds of -0.3 to +0.3 with respect to the CSI.

 

[JoeMX82]

Thanks to all for the advice - going to lower TA and go from there.