FC Levels low daily

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sharonaliza

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May 30, 2015
13
Seattle, WA
I'm not sure if I need to add CYA or what, but my FC levels are low every night. I test every evening after we're finished swimming and then add bleach. My levels get down to 1.5-2.5 generally. It's been a bit cloudy and we've had a lot of kids in the pool, so someone suggested getting it up to 10 the day before and the day after big parties. That had helped with the cloudiness, but the FC still gets low. Am I understanding correctly that it should not get below 4?

Last night's #s:

FC 1.5
TA 90
CYA 45
Ph 7.5

I tested a couple hours after I put in the bleach and the FC was 10.5. This morning it was 9.5. Tonight, after only me swimming, it was 2.5

It has been Hot here in Seattle (90+), which is unusual for us. Is it possible I should raise the CYA? Should I just try to get the FC levels up higher in the evening?

Is the end of the day the best time to test, or should I test earlier?

Thanks all for your help!
 
If I understand you correctly, you lost 7 ppm of 10 ppm between doses, in less than 24 hours?

You may be battling a nascent algae uprising with that kind of chlorine demand, which may have been caused by letting it drop below 4 ppm. Either that, or you have an unusually high usage rate due to organics or something else, like a pesticide spray, getting into the pool fighting the chlorine (unlikely, since your above ground.)

In either case, I think you should do a careful overnight chlorine loss test first to confirm how much you lose overnight with no sunlight (see details in How to Slam in my signature). I believe a SLAM -- which, if your water is clear, will likely be a fairly short one -- will get you ahead and thus reduce your daily chlorine use.

Even if you loose less than 1 ppm overnight, riding the chlorine higher for a few days may help. Also leave the filter running with the higher FC.

Your CYA should be fine at that level...I'd start with increased chlorine and not letting it drop first, then if the consumption rate continues, explore the cya avenue further.

Re: best time to dose...the benefit of night dosing as you're doing is more chlorine stays in at night with no sun to burn it off...so you're pretty much doing the optimal time. I dose in a.m. Just because that's when it's consistently convenient for me ;)
 
Thanks so much! I'll do that tonight. I've had trouble with algae in the past, but it was usually at the end of the season or when it was cloudy and cool. I have had some trouble with cloudiness, but I have been upping the FC at night to 10 when I know we'll have a lot of swimmers. Hopefully the SLAM will help!
 
So, I'm confused about raising the FC. I had a FC of 4.0 today after no one had been in the pool. I used the calculator to raise it to 16, per the chart. It said to at 86 oz of bleach. I tested two hours later and the FC is 27.5! Is it supposed to go that high?
 
If your testing is accurate I would say that either your chlorine is stronger than the % you used in poolmath or your water capacity is incorrect. 4800 gallons in a 9x18 pool would require a water depth (not wall height) of 48".

Reducing all those dimensions by 6" (8.5' X 17.5' X 3.5') brings capacity to 3900 gallons.

Dom
 
Dom, you're absolutely right about the pool capacity. It hadn't occurred to me to change that! I did check the % on the bleach, which is correct.
The FC this morning is at 16.5 - quite an overnight loss. I'll keep testing to keep the FC up to 16 (using the correct capacity!!) throughout the day.
 
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