High FC loss overnight!

[rme]

Morning!

Thought I was doing great & decided to do OCLT last night. FC level went from 7ppm last night to 3 ppm this morning and CC=1ppm (it's been o or .5 all week) ugh... :grrrr:
So I just shocked the pool according to the FC/CYA chart to get FC levels up to 12.

FC: 3
CC: 1
pH: 7.5
TA: 100
CYA: 30ish

Pool water looks & feels great, no slimy walls so I don't understand what happened. We've had company the past few days, so there have been extra people in the pool. My lowest FC read was 2.5 one afternoon, other than that it's been between 3-4 during the day and we bump to 7 at night.

We are new pool owners (I posted last week in Just Getting Started to make sure we were starting off on the right path) and have used BBB method from day 1.

Is this something I should expect after rigorous use? Is there a way for me to be more proactive? I just cringed this morning as I poured all that bleach (250 oz) into the pool.

As always...you guys rock! Thanks for all your help.

 

[PoolGuyNJ]

Shock the pool. The CCs are too high.

Scott

 

[Richard320]

Are you sure nobody snuck out for a midnight skinny dip?

 

[rme]

Tested about an hour after shocking:

FC: 12.5
pH: high (possibly 8)
TA: 90
CYA: 30-40 (seems higher today than yesterday, we added CYA Sunday night...)

I did not do CC test. According to Pool School I should shock at least twice, so I plan on doing that again tonight. I'll perform all tests again prior to shocking.

Should I be concerned about high pH reading? I was reading around the site and consensus seems to be no- pH tests are inaccurate during shock levels.

Any reason the kids shouldn't use pool this afternoon- I shocked around 9am?

 

[WestSidePool]

To be proactive, add enough chlorine before your swim party to keep it above minimum, and test during if you have to.

Keep in mind, shocking is a process. You have to keep your chlorine level up at shock level until you pass the three tests, otherwise your just wasting chlorine.

-CC is 0.5 or lower
-An overnight FC loss test shows a loss of 1.0 ppm or less
-And the water is clear.

It's safe to swim while shocking as long as the shock levels are at the recommended level with your CYA.

 

[Richard320]

pH can read wrong with high FC levels. Ignore it for now.

 

[rme]

Thanks for the feedback. 1 pm test results show :

FC 11.5
CC .5
pH 7.5- 7.8

I feel better now. I did vacuum and backwash. I'm thinking that may also impact results but am not sure.

 

[linen]

CYA: 30-40 (seems higher today than yesterday, we added CYA Sunday night...)

CYA can take up to a week to show up in the test. I would use how much you think you put in to calculate your shock level for now. Test CYA again this coming Sunday/Monday and then adjust your FC levels to that.

 

[frogabog]

Now is the time to add .5ppm chlorine to raise it back to shock level.

Falling below minimum even ONCE can cause this (happened to me about two weeks ago). The prevention is to never let it get that low, if you have to add a little more for high bathing load do it. It sounds like you caught it early enough to make it a one day shock process. But don't let it fall below shock (12ppm). Maintain shock level through today, do an OCLT with CC tomorrow morning and it will likely be all done. If not, one more day of maintaining won't hurt.

 

[anonapersona]

I'll bet the pool was digesting sunscreen and that is what consumed the chlorine.

 

[rme]

Now is the time to add .5ppm chlorine to raise it back to shock level.

Falling below minimum even ONCE can cause this (happened to me about two weeks ago). The prevention is to never let it get that low, if you have to add a little more for high bathing load do it. It sounds like you caught it early enough to make it a one day shock process. But don't let it fall below shock (12ppm). Maintain shock level through today, do an OCLT with CC tomorrow morning and it will likely be all done. If not, one more day of maintaining won't hurt.

I did not realize that when shocking I had to maintain the shock level throughout the whole day or time frame. I'll definitely keep that in mind from now on. For now I think the problem's been resolved.

Thanks for everyone's help during my crisis!