Chlorine gone overnight

[revkevinhale]

I have pool in ground, vinyl lined pool that is 19,200 gallons. I've been faithfully testing and adding the appropriate amount of chlorine daily using pool math. Pretty much everyday I have to add 2qts, 1cup, 2oz to get my chlorine back to where it belongs.

Normally, I do this around 700AM. Today, I did it around noon. When I tested the water, there was no free chlorine and the combined was less than .5, like it normally is. I say, less than .5 because using the TF Test Kit when I add the chemical in to turn it pink again after testing FC, there is only the lightest perceptible pink tint to the water. It could easily be mistaken for clear. This is basically what it is everyday. Anyway, today when I tested the chlorine about 5 hours later than normal, there was suddenly no chlorine at all.

Is five extra hours of morning sun enough to zap the rest of my chlorine like this, or should I be looking for another solution?

Peace,
Kevin

 

[JoyfulNoise]

Depends on CYA level but it looks like yours is around 50ppm (we round up CYA on the test, you can't get 45ppm ... the scale is not linear) so no, the sun would not burn it all. Sounds more like your FC level drops way too low and that allows algae to get a hold. You need to do an overnight chlorine loss test to see if something is growing. If you fail that then you need to SLAM your pool to fix the problem

 

[ajw22]

Your PoolMath logs show your FC dropped below the minimum for your CYA level a few times. Algae may have taken hold in your water.

Do a Overnight Chlorine Loss Test and if you fail then follow the SLAM Process.

 

[revkevinhale]

Thanks guys! I'll do that tonight!

 

[tstex]

what type of filter do you have, when have you cleaned it last and what is the PSI reading w your avg pump speed, ie 2500RPM

 

[revkevinhale]

Alright,

I only lost .5 overnight. So that's good.

However, two things piqued my interest. 1) Allen noted that my levels were dropping below the minimum occasionally. This seemed odd since I test and add chlorine using the recommended levels in the app daily. 2) Last night I used the app to bring my levels up to ideal, waited 30 minutes, and tested again. My chlorine level should have been at 6 when I tested, but they were at 4.5. I remember noticing a similar phenomenon when I SLAMed my pool at the beginning of the season.

In light of these two issues, I figured I either had a very serious problem that was eating 1/4 of my chlorine in 30 minutes even though I still had crystal clear water and virtually no combined chlorine, or my volume was wrong. The latter theory had more explanatory power, so I measured my pool and put the numbers in the pool math form. My volume is 21,100 not 19,200 like the pool shop told me the first summer I had the pool. That probably accounts for at least some of the issue because I was never getting my chlorine as high as I thought I was. I suppose that does not entirely rule out a very serious problem, but an overnight loss of .5 and being under by 2000 gallons on the volume at least explains some stuff.

tstex - My filter is a Pentair Sand Dollar High Rate Sand Filter model SD-70, and my pump is a Pentair Superflo High Performance Pump model 340039. I backwash the filter at least weekly. The pressure on the pump's gauge is at 20psi, and it pretty much stays there. The sticker on the pump says 3450RPM.

Thank you all for your help with this!

Also, Matt, thanks for the CYA tip. I missed that in the pool school reading I did.

Peace,
Kevin

 

[tstex]

Thx Kevin, sounds like your empirical data is being cleaned up.

If your filter pressure was up considerably and you had also recently cleaned it, then dead algae could have clogged the system…doesn’t take long.

W your new vol’s, repeat the procedures a d compare your figures

 

[ajw22]

That probably accounts for at least some of the issue because I was never getting my chlorine as high as I thought I was.

Also the % chlorine in your jugs may be less then advertised.