raising a low pH

I have a 12,500 gal inground vinyl pool with sand filter, just opened 3 days ago. A little dirty at first, but looks great now except for some algae on the liner above the water line that I am gradually toothbrushing away. CYA level was zero at opening, so I added 2 lbs of CYA in a sock which just finished dissolving this afternoon. Checking the chlorine level three times daily, I either get 1 or 0. Each test is followed by adding 1.3 gal of 6% chlorine (total of about 15 gallons so far). TA is 100. pH has dropped from 7.4 to 7.0 over the past several days. I would like to raise the pH with Borax. Is there an equation (or expert advice) to determine how much Borax gives how much pH rise per 10,000 gallons at a given TA? Does the stuff dissolve easily, like baking soda, or do I need to get out the CYA sock again?

Thanks in advance.

Searched the site for this issue without success; I apologize if it has already been discussed elsewhere.

Welcome to the forum.
You need to get the chlorine up. You're on the right track. As for borax, it and baking soda dissolve easily and fast, unlike CYA. Just throw it in the skimmer and let the sand filter handle it. Will probably dissolve in 10 minutes or less. One member 'mwsmith2' has a calculator you can download that has all the calculations you'll need....I believe. Look for one of his posts and the link to the calc is in his signature. The fact that you're eating up chlorine so fast says there's somethingin there still being oxidized so just keep at it. You want to get to around 12-15 ppm or so and hold it there for a couple days. Someone else can kick in here from the chemistry side. Sounds like you aren't getting the chlorine concentration high enough to kill the stuff and you're not getting ahead of the battle.
A question...what kind of test kit are you using?
Hope this helps.
Al

Hi, Boomer,

A four pound box of Borax changes my pH about .2 My pool is 43k. One pound in your pool would make sense. Give it 12-24 hours and test. It dissolves quite easily poured directly in the skimmer (pump running) and may take effect much sooner than the 12-24 hours...I've never tested.

A comment on your CYA. It seems you will come up with a CYA of 20 using 2 lbs.....safe but perhaps a little on the light side. If it came in a 3lb container, I'd put the rest in hoping for 30ppm, Many folks run in the 30-50 range.

It also seems to me you're not dosing heavily enough on your Cl. I would recommend putting in twice that much (12ppm....maybe even 14ppm) just before dark and then testing in the morning to see how much residual Cl is left. If it has dropped significantly, I would bring it back up to the same level the next evening and again the next, until your 12-14ppm holds overnight. Then let your Cl drift down into the 3-6 range for the rest of the Summer. This will ensure your water is sanitized and not retaining any algae "bugs"

More info than you asked for, I know, but hopefully useful.

Thanks for your comments and advice, Poconos and duraleigh.

I added about 4 lbs of Borax in increments over the past two days without any movement in pH. (I wonder if this was because the Borax had been sitting open in my laundry room for the past seven years.) Switched to pH Up (sodium carbonate, HTH brand) from Wal-Mart and about one pound has me back up to pH of 7.5

With a little more CYA, chlorine is now doing great as well. TA is right at 100, so I'm good to go. I use Ben's kit, of course.

BTW, the posted pool chemistry calculator requires PC Windows to run, unlike the Excel file last year for simple chlorine calculations. For us Macintosh users, nothing comparable that I can find.