Ph not checked before adding bleach...

[triplets&quads]

We have a really bad algae bloom in our pool in the middle of winter!! We've had temperatures so cold that my husband disconnected the lines from the filter and the pump to keep them from freezing, so there has not been any bleach added to it for a couple of months. And of course we removed the SWG too, but it doesn't work at low temps anyway. Now, almost all of a sudden, the pool is green!! I had my husband hook the pump and filter back up today and bought a boatload of bleach to add to the water. My problem is, my husband added the bleach before I tested the water and I have no idea what the PH was at the time. What do I do now???? I got a water sample (hours after the bleach had been added) and the PH is thru the roof! 3 3/4 gallons of bleach was added to the pool per the pool calculator. The FC is 15. CC is 0. I haven't checked the TA.

 

[chem geek]

High FC will usually make the pH read unusually high. At this point, I would not worry about it until after you are done shocking.

 

[triplets&quads]

THANK YOU chem geek! I was hoping it was going to be ok!

 

[guamguy]

Sorry for the hijack, but how high does the FC need to be in order to throw off the pH test?

 

[chem geek]

About 10 ppm, though this depends on things like the TA level. The quote from Taylor's Pool & Spa Water Chemistry booklet on this issue is as follows:

FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purple color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.

When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.

 

[guamguy]

Thanks!

 

[triplets&quads]

My FC held all night and day and instead of being a green mess, the water is looking good! You can see piles of dead algae on the bottom, so now I have to get the vacumm in the pool. Because the chlorine is still high, I didn't check the ph or TA. I will test again tomorrow before the big rain hits us.

Can you get an accurate reading for TA when the chlorine is at shock level?

 

[JasonLion]

Can you get an accurate reading for TA when the chlorine is at shock level?

No, not really. The TA level should read the same with high or low FC levels. Sometimes the colors you see during the TA test are different at high FC levels, but the reading should be the same.

 

[triplets&quads]

Yesterday I thought my FC had held at 15 overnight, but that wouldn't be possible would it, if it was killing algae, right? So I am thinking when I counted my drops, I forgot to divide by 2, so my reading from last night would have been FC 7.5 and not 15!! Tonight it is FC 5.5, so I am wondering if I held it at shock level long enough or should I bring it back up to shock level?

FC 5.5
CC 0
TA 60

 

[Bama Rambler]

The criteria for knowing when you're done shocking are,
1) When you lose 1ppm or less FC overnight.
2) When you have less than 1ppm CC. and
3) The water is crystal clear if you don't have a fas-dpd chlorine test kit.

You run the FC test after dark and again the next morning before the sun is on the pool.