How long to wait between ph tests when adding borax

[Runningfan]

Hello. First, let me thank this forum for helping me successfully manage my first summer of pool ownership. I have learned so much through reading the Pool School and hundreds of posts that have been made on a wide variety of subjects!

I am attempting to help a friend SLAM her pool to get rid of an algae attack, and we need to bring her ph level up first.

How long after we add the borax can we accurately re-test the ph levels again? I think I read somewhere on here ~2 hours, but I can't seem to find that piece of information now...

Thanks so much!

 

[linen]

Welcome to tfp, Runningfan

We generally recommend waiting an hour between chemical additions before testing again and redosing.

What is her ph now? What is her TA now? What is her cya now?

 

[Patrick_B]

Welcome to the forum!

 

[Runningfan]

Thanks, all!

FC = 22
CC = 1
TC = 23
pH = 6.8
TA = 100
CYA = 100+
CH = 320

Using the tablet chlorine, so that is why CYA is so high and pH is so low...

 

[Runningfan]

And she is borrowing my TF100 test kit.

 

[spidey07]

He aware ph test isn't accurate above FC of 10

 

[ping]

This pool needs some work before SLAMming it. The pH should have been raised before adding the chlorine because the pH will read higher than what it is when the FC is above 10. Trying to SLAM a pool with the CYA 100+ is going to be a tough process.

Test the CYA level again by using half pool water and half tap water. The test result will then be about 1/2 of the CYA level. So if the test reads 70, then the CYA level would be 140. Doing the CYA test this way will let give you a better idea of how much water will need to be drained.

You should drain some water off to lower the CYA level to 50 before SLAMming as this will make the process much easier to complete.

 

[Runningfan]

Thanks for the help!

Yes, my understanding is that the pH test tends to read low when the FC is over 10, so we suspect it may be even lower than 6.8. So it definitely is what we're trying to fix first.

We also know the CYA is really high and will need to come down, but refilling the pool is very costly here, and she had planned on closing this weekend anyway. It will be cheaper in this instance to just raise the chlorine levels up (WAY up) to kill the algae before she closes. Then next summer, she will drain and refill and bring down the CYA and start the season out on the right foot.

Ping, thanks so much for the tip on the 1/2 and 1/2 CYA test. All we know right now is that it's over 100...that's as high as the test goes. So that will be helpful in getting a more accurate read.

 

[Bama Rambler]

I think that the pH actually reads higher than real when the FC is high.

 

[spidey07]

Yes it does. It may be a good idea to up the ph in this case during slam if closing. Don't want acidic water sitting closed. Or let FC drop below 10, get accurate test and adjust properly.

 

[Patrick_B]

Yes. False high pH with the phenol red pH/color block test and >10 FC.

 

[ping]

Let the FC drop below 10 and adjust the pH to 7.5 then close the pool. I would not bother trying to clear it up since it is going to be closed so soon.