Balancing PH in a new plaster pool

[bchifor]

This spring we had to redo our 24000 gallons plaster pool (removed all the old plaster, fixed some cracks, re-poured the bond beam, tile, coping, new plaster). After 30 days I installed a SWG chlorinator (Circulpool Universal 40) and added enough salt to get to a 3500 ppm salinity. This measurement is reported by both SWG and a salinity measurement pen like device. I've been in the past following the TFP method without too much stress. I checked the water with test strips, and balanced PH first, chlorine second and didn't worry too much about calcium or CSI. However, with the new pool, I want to make sure I stay on top of all chemicals, to give the plaster a long life. So, I got the TF-100 test kit and started to do daily PH and Chlorine tests, and weekly alkalinity and calcium hardness. I'm struggling a lot with the CYA test, but I'm relatively sure the value is about 60-62. My biggest issue is the PH, I'm having to add muriatic acid every 2 days. I only add 1/2 gallon at one time. I use the HomeDepot HDX brand (14.5% hydrogen chloride). One day my PH would be 7.5, the next is 7.8 and the next one is above 8.0. That's when I add another 1/2 gallon for 2 nights in a row (basically 1 gallon in total) to get it back to 7.5. Alkalinity has been decreasing steadily from 110 to currently 80.

Here are the results of today's tests:
FC: 5
TC: 5
PH: 7.5
TA: 80
CH:400
CYA: 62
SALT: 3500
TEMP: 79.5
CSI: -0.24

According to Pool Math, everything is good (CYA and TA are outside of ideal range, but that's about it). The water looks amazing, perfectly clear and blue.
However, based on experience I know tomorrow PH will be 7.8 and the day after >8.0 if I don't do anything.

I've also heard that new plaster and new SWG will quickly raise PH, but I'm not sure if this is in normal parameters. I'm currently adding 2 gallons of 14.5 muriatic acid to the pool every week.
Also the second part that's confusing for me, lots of non TFP people tell me that my TA is way to low and that's why the quick raises in PH, but Pool Math wants me to lower it more.

Also I've done a test at Leslies, just out of curiosity, and most results came back similar to mine, except they measured the TA at 53 and the CH at 300. I'm trusting my TF-100 kit for now, but I'm a bit confused on why I can't get a handle of my PH and the behavior I'm seeing does in a way match what the "non TFP" workflows suggest, my TA is too low and so I have no PH buffer.

And finally, if this matters, we are in SoCal, the pool is clean, brushed and vacuumed at least weekly.
This PH thing is driving me crazy, any ideas on this forum ?

 

[cdadams1223]

Keep your pH between 7-8 and if it goes over 8 then dose it with MA per PoolMath. Your TA will eventually settle and be in equilibrium with your pH. You could even let your TA drop to 50 which is fine. Don't add MA if your pH is still in the 7s...just wait until it hits 8 or >. Also, no need to report total chlorine (TC). At TFP, the only chlorine related measures to post are FC and CC (combined chlorine or chloramines). Another thing to remember re: CYA is the testing scale is logarithmic. You cannot have a CYA of 62. Bump that up to 70. With that said, your FC target range is, per FC/CYA Levels, 8-10ppm with a minimum of 5ppm. Your current levels are too low and you need to get some more FC in your pool. Per PoolMath, you need to add 1.2 gallons of 10% LC or 1 gallon of your 14.5% LC. I don't think I've seen LC strengths greater than 10% or 12.5% that you can purchase at a store.

 

[cdadams1223]

Meant to add earlier that if you can, try to grab some 31.45% (20 Baume) MA. You'll end of requiring less. A gallon of 14.5% lowers your pH by 1.3 vs 2.6 with the 31.45%.

Also, trust your TF kit. It is waaaaay more accurate than any Leslie's et al store will provide you.

 

[midlifecrisis]

The a acid home depot sells is 31.45% (20% be). I do not belive they have any other concentration so please check your numbers.

 

[midlifecrisis]

Also, I struggled with my new pool as well,and 6 months in, still am, but it is slowing ever so slightly. I'm not sure where you're located, but check pressure washing businesses and other commercial cleaning supply places and you might be get lucky and snag a cheaper price even it it requires a bulk purchase. You're going to use it, and it doesn't degrade like chlorine.

 

[Bperry]

Also the second part that's confusing for me, lots of non TFP people tell me that my TA is way to low and that's why the quick raises in PH, but Pool Math wants me to lower it more.

Welcome! This is exactly backwards. Having a high TA causes faster pH rise. Your TA can safely go down to 50ppm before your pH starts to get unstable and could crash too low so keep it at 50 or above. The only reason to even monitor TA is to help keep the pH stable.

The reason the non-TFP sites push for higher TA is because they tend to use trichlor tablets which are acidic and drive the pH down over time. So they need higher TA to keep the pH from crashing too low.

That’s also the reason people think a SWG raises pH, but it doesn’t. It just seems that way because they’ve stopped using pucks for chlorination and don’t have its pH lowering properties any longer.

Also, you may find your salt chlorinator to have trouble keeping up. The manufacturers spec their compatible “pool size” as if you run it at 100% for 24 hours per day. TFP has found that getting a SWCG rated for twice their pool size tends to work best. You may find that you need to supplement with liquid chlorine in the heat of the summer unless you run the equipment at it’s max.