Why can't I get my ph to stay down?

[tjm5837]

Last month replaced half my water due to high cya. Now can't seem to stabilize my ph below 8. Todays readings are typical:

Temp 82F
FC 3
TC 3
CC 0
ph 8
tot alk 100
ca hard 280
cya 39
sat ind 0.52

I add muriatic acid to bring down ph range to 7.4 for a day, but by 48 hours it's back up to 8.0. Adding all the acid brings my tot alk down so end up having to increase it with sod bicarb but having to add the acid so often just brings tot alk back down again. I feel like I'm chasing my tail.
My pool builder recommended tot alk of 120 to 150 and calc hard of 250-350 and stabiliser 30-50 pH of 7.4 to 7.6. Seems like I can keep pH more stable with a lower Tot alk (like 80 or so)

What's better for the pool? normal ph or tot alk in range recommended by builder? That is if I could pick only one.

By the way pool water looks and feels great. (wouldn't know there's a problem)

 

[JohnT]

How old is your pool surface?

Do you have any waterfalls, fountains, deck jets etc. that result in aeration of the water?

 

[tjm5837]

12 year old surface. Still great condition. Have a spa spillover and a waterfall. Have been keeping the waterfall off due to airation.

 

[aa62579]

Here are the numbers recommended by this site in Pool School. They seem to match what you have seen in practice.

"If you have a SWG, or if you commonly run water features such as a spa, waterfall, or fountain, keep TA on the low side, between 60 and 80. Otherwise levels between 70 and 90 are good. Pools with plaster surfaces should factor their CSI into the preferred TA level decision."

 

[anonapersona]

The builder recommended TA 120-150 assuming you are using trichlor pucks.

TA of 80 or even 70 may work best for you if you are not using trichlor pucks. I try to get to 70 but my tap water is high TA so it is a constant job to keep TA in line.

 

[tjm5837]

Yeah I don't use the pucks anymore since the water change to get rid of the cya. So I take it there is no real problem letting the TA go to 70-80, if that's what keeps my pH consistent?