swimming and muriatic acid

[mohawk]

We have a 20,000 gal ag pool with 220 alk and 7.8 ph. I want to try to lower the ph and aerate for the alk, but I wonder, how long do we have to wait to use the pool again? We live in Minnesota and are not to accustomed to the 90+ degree weather we're having. The family would not be happy with me if they couldn't use the pool every day. Any thoughts? Denise

[chem geek]

We have a 20,000 gal ag pool with 220 alk and 7.8 ph. I want to try to lower the ph and aerate for the alk, but I wonder, how long do we have to wait to use the pool again? We live in Minnesota and are not to accustomed to the 90+ degree weather we're having. The family would not be happy with me if they couldn't use the pool every day. Any thoughts? Denise

If you are asking how long it will take to get your alkalinity down, that depends a lot on how well you will be able to aerate your pool water. I assume you will follow Ben's guide to Lowering Alkalinity in which case you will get faster results if you can lower your pH as much as possible but not lower than his 6.6 limit. Your test kit may not register that low so that is probably where you will be most limited (be sure to follow his instructions to not go to the lowest pH color on your test kit because you won't know how much below you are if you do).

Once you've finished Ben's procedure, there's no waiting time necessary.

If anyone else has actual experience with how long it took to lower their alkalinity, please chime in. My guess is that it will take more than a day to drop from 220 to, say, 120 or so.

Richard

[KurtV]

Denise,
So long as you keep the pH at a reasonable level you can keep using your pool during the alkalinity lowering process. In fact, one of the ways Ben recommends aerating the pool is with a group of rowdy kids. At any rate, you should keep the pH one step above the lowest level your test kit can measure to ensure that it doesn't go really low (since 5.0 or 6.0 will look much like 7.0 if 7.0 is the lowest your kit will measure).

You can swim almost immediately after adding acid; it gets diluted very quickly. If you're worried about it, distribute the acid around the pool as you add it or give it an hour with the pump running between adding acid and swimming.

[chem geek]

Kurt's absolutely correct. I forgot that kids splashing made for excellent aeration and that you needn't go down to 6.6 to lower your alkalinity -- you can go to the lowest on your test kit, probably 7.0 as Kurt surmised, and that is perfectly safe to swim in. It might take a little longer to lower the alkalinity compared to lower pH (though even 6.6 might only just sting the eyes), but since you're using the pool in the meantime, who cares? Thanks Kurt.

[mohawk]

Thanks for answering so quickly-I didn't want anyone to be harmed from the acid once I put it in. I think from other posts I read the process of lowering the alk is slow, but I have lots of time. Denise

[chem geek]

Thanks for answering so quickly-I didn't want anyone to be harmed from the acid once I put it in.

Just so you have even more piece of mind, I recently did an experiment to see how quickly chemicals would diffuse throughout the water and therefore how quickly they would be at safe levels. I put in some "Party Blue" dye at the return jet in the deep end of the pool and within a few minutes, it was spread throughout the deep end. Then, it got sucked into the two floor drains and into the skimmer and then started streaming out of the jets at the shallow end of the pool. The pool was full of color in less than 10 minutes and I didn't notice much change at all after 15 minutes. I think if you want to be very conservative, then it will be absolutely fine swimming after 10 minutes; 15 tops, but in practice it's probably fine after 5. This assumes you've got good circulation in your pool.

Richard

[waterbear]

Brushing the pool after adding the acid (or any other chem) will also help it to mix faster.