pH shot up with just two cups of borax!

[IGnatius T Foobar]

Hey everyone, I've got a weird pH issue. Running a 3871 gallon Intex vinyl pool with a SWG, and the pool water has remained (and still is) crystal clear. Initially I had trouble keeping the chlorine level above 1, but after 1/3 pound of dichlor and continued daily operation of the SWG, it's staying in the 4 to 5 range.

My problem is pH. It's always been on the low side, 6.8 to 7.0. Yesterday I added about a cup of borax and it barely budged. Today I added two more cups and it shot up to the 7.8 to 8.0 range. Testing was done about an hour after application. What did I do wrong? Browsing around this board I see people adding entire boxes of the stuff and barely getting results. Did I just not wait long enough before doing the second test?

Additional information: I added the borax by slowly sprinkling it in at the return jet (because I don't have a skimmer basket). I am testing chlorine and pH using the HTH 3-way test kit.

[AnnaK]

Size matters

Putting a whole box of 20 Mule Team in a 20,000 gallon pool is different from putting 3 cups in 3,800 gallons. Do you know what your total alkalinity is?

[IGnatius T Foobar]

TA is 120. After 24 hours pH is still hovering around 8.

[AnnaK]

TA is good. Do you still add dichlor now and then? That will help lower the pH a little. It also will raise the CYA (stabilizer). Do you happen to know what that number is for your pool?

You can get a small container of "pH Down" or "pH Minus" at the pool store. It's dry acid. The instructions are on the container and are probably given per 5,000 gallons so you'll want to use less. A good rule of thumb is to use 1/2 of any chemical, wait a couple hours, test, adjust.

We have a Sticky for using muriatic acid to lower pH but it involved buying a gallon of acid and you'll never need that much over the life of your pool. The dry acid product from the pool store is more suitable for your situation. It's not expensive, it's easy to use, it stores well across seasons, and for small systems it's more efficient. Just go easy on the amount.

[IGnatius T Foobar]

I haven't added any more dichlor because the SWG has been maintaining the chlorine level just fine without any help. But if it will lower the pH a little then I will give it another small dose. Unfortunately I do not have a CYA test.

Thanks for the dry acid suggestion. Buying a supply of muriatic would definitely be overkill; this is a seasonal pool and I really only need to get through the next five weeks or so. The water is already beautiful, so I just want to keep it safe and avoid doing anything that would wear down the liner so I can put it up again next year.

[aylad]

Rising pH is also an effect of the operation of the SWCG, and is something that you'll always see as long as you use it. If you'll drop your TA to the 70-80 ppm range, and drop your pH to 7.6, it should help it stay more stable, although it won't stop the rise altogether. Adding acid on a routine basis to combat the pH rise is one of the only water maintenance issues with a SWCG.

Janet

[IGnatius T Foobar]

yeesh ... I can't win. I added dichlor and dry acid at half the recommended amount for my size pool and my pH swung all the way back down to the acid end of the scale. Dunno whether I should try microdosing with borax or what. Would leaving the cover off (particularly during a rainstorm) tend to raise or lower the pH?

[aylad]

Aeration of the water, and operation of the SWCG, should both work to raise pH. However, if it's below 7.0 now, you need to get it back up above 7.0 ASAP using small doses of borax. Aeration doesn't work quickly enough when the pH is dangerously low.

[BigDave]

...Would leaving the cover off (particularly during a rainstorm) tend to raise or lower the pH?

As aylad suggests, aeration (raindrops) will tend to raise pH but, in my pool, rain usually lowers pH (acid rain). Definitely follow aylad's advice and bring the pH back up with small amounts of Borax.

[IGnatius T Foobar]

How small?

What's the correct dose of borax to move the reading just a little bit on a 3861 gallon pool?