how much acid

[not2high2fly]

I have about 27,000 gallons and my ph is off the chart,i have some acid from a motorcycle battery i never used any ideas on how much to start with? Thank you

[PoolDoc]

Do NOT use the battery acid!
Do NOT use the battery acid!
Do NOT use the battery acid!
Do NOT use the battery acid!
Do NOT use the battery acid!

Oh, yeah, do NOT use the battery acid! If it's ever been in a battery, it will poison you, in your pool. If it hasn't, it may, or may not, be pure sulfuric acid. You could use pure sulfuric acid to LOWER the pH in your pool, but you don't know that battery acid doesn't have 'additives' in it for batteries, but not for pools!


Back to the original problem you mention: is your pH off the chart LOW or off the chart HIGH? If it's HIGH (over 7.8) you need acid. If it's LOW (below 7.0), you borax or washing soda.

[not2high2fly]

The acid is pure sulfuric acid brand new never opened. And my ph is high.Thanks

[PoolDoc]

As long as it's pure sulfuric, it's OK. Not as good as hydrochloric, at least for concrete pools, but one dose won't cause problems even there. Use small doses, however. I have no idea what the strength is, compared to standard muriatic.

[not2high2fly]

Got back from walmart a few hours ago picked up the hth 6 way test kit(it was the best one they had) and the last 7lb bottle of hth ph minus. My chlorine and ph are high(off the scale) the TA was around 150 and it only turned the blue to a pale red on the test kit so maybe a little higher. On the total hardness test the water didn't turn red but did go to blue after 10 drops so i guess 100ppm and the CYA was 90ppm. Just did a vacum to waste and a long backwash to dump some water(couple hundred gallons), should i add the ph minus or keep dumping water? Thanks for your time and help

[PoolDoc]

I guess I'm going to throw the question back to you: it depends on whether you want to run a high CYA pool or not.

Read the Best Guess page linked in my signature. If you keep the high CYA, you'll have to run the chlorine levels shown. It scares some people to run FC that high, though there are no ill effects on outdoor pools that we've been able to discover. And you tend to use less chlorine, and certainly don't have to dose as often with a high CYA / high Cl pool.

Personally, I'd run high CYA, high Cl, rather than dumping all the water. But it's up to you. The 'classic' BBB method I developed assumes lower CYA levels.

You'll either have to run the chlorine levels shown OR lower your CYA. If you want lower the CYA, you'll need to replace 1/2 of your pool water. If you do drain, do so safely. Inground vinyl pools can't be drained without professional help; inground concrete pools in low or wet areas can 'float' out of the ground, destroying the pool. AG pools shouldn't usually be drained completely -- but 6 - 12" of water left is usually safe.