raising a stubbornly low pH

[wilcfr]

Here are the particulars:

gunnite inground pool
38,000 gallons
TA 119
Chlorine 3ppm
Calcium 240
pH 7.01
Temperature 87

I test chlorine(dpd), TA(titration) and hardness(titration) with Hach Kit water testing kits and pH and TDS with handheld meters

We had to add a good bit of dry acid to get our TA down from 300 to 119. This was done over a period of 2 weeks. The pH dropped to 6.67. We added 4 boxes of Borax, which over the course of a week only brought the pH up to 6.8(we have been using the Borax for a couple of years and don't seem to have the luck with it many of you on this site have). We have since added 10 lbs of soda ash over a period of 3 days and gotten the pH up only to the 7.01 level. From what I have read on this forum and website the Borax should have raised the pH considerably more than it did, and based on a number of online pool chemistry calculators the 10 pounds of SA should have raised our pH to around 7.3-7.4. We use 3 inch trichlor in an automatic chlorinator and shock with either calcium hypochlorite or sodium hypochlorite. The pool as been shocked once using the calcium hypochlorite. Any suggestions as to how best to raise the pH another 2-3 points without blowing the TA out of wack again? And any guess as to how long it should take? The pool is clear and swimmable, but I would really like to get the pH up for a variety of well accepted reasons. We always battle the TA problem early in the season, last year it took 4 weeks, a lot of acid and a subsequent drop of pH down to 5.5 to get it down from over 300 to a reasonable 190.

Thanks