1. ## FC

Hello to all.

Is there an "average" FC a pool should loose over the course of one day? Assuming a very light swim load (usually only 2 adults), and direct sun on the pool during daylight hours I'm just trying to gage what normal liquid chlorine additions would be over the course of a week. I know Pool Math will get me where I need to be numbers-wise, just curious if there's an FC drop "cutoff" of some kind where I should be on alert that there may be a potential "problem" on the horizon. Thanks.

2. ## Re: FC

In a clean pool ... 2-4ppm per day is normal, depending on sun exposure, water temp, etc.

3. ## Re: FC

Thanks Jason. Should 5 ppm be a cause for concern, assuming zero swim load and the things you list above?

4. ## Re: FC

Maybe ... there is no hard number. If your CYA is too low and you have a lot of sun, then 5ppm may not be surprising.

5. ## Re: FC

Thanks again. Assuming CYA isn't low (below 30), would it make a difference (regarding FC loss) if the CYA were 30-50 (ideal) or 50-70 (higher)? This is assuming of course the FC level is at the appropriate number based on what the actual CYA is. Just curious; still in the learning process.

6. ## Re: FC

The higher the CYA and the lower the sun exposure and debris load, the less FC you should lose in a day.

For example, made up numbers, but should give you an idea:
If your CYA was 30ppm, your minimum FC is 2ppm, you may target 5ppm and lose 3ppm in a day
If your CYA was 60ppm, your minimum FC is 5ppm, you may target 7ppm and only lose 2ppm in a day

So with a higher CYA, even though you have to maintain a higher FC level, you actually lose less each day.

7. ## Re: FC

Got it Jason, thanks. So if my CYA is 70 (which it is) and I have a 5ppm FC loss (which I did), there may be a problem?

8. ## Re: FC

Maybe ...
CYA protects a % of the FC. If you have a CYA of 70ppm and FC drops from 8 to 3ppm in a day, you have a problem. But, if you started at a FC of 20ppm and it dropped to 15ppm, that could be normal.

9. ## Re: FC

Thanks. I did just come off of a SLAM and am letting the FC drop naturally (for the record it went from 15.5 to 10.5). I will keep a close eye on it since I do need to keep it btn 5-8 for my present CYA. Thanks again.

10. ## Re: FC

That could be normal. Only a 33% loss. I would guess you might be around 7ppm the next day

11. ## Re: FC

I realize my comment is late, but one other parameter you are neglecting to think about are combined chlorines.

Free chlorine can bounce around quite a bit and I've seen some weird day-to-day variations in my pool. But I always know when there is a problem when I see FC fall and CCs rise - that tells me that something is growing, getting zapped by the chlorine and then breaking down into CCs.

So keep an eye out on your CCs as well. If you see them spike, that could also indicate a problem.

12. ## Re: FC

Thanks Jason.

Thanks SunnyOp, no such thing as "late" for me. I'm still absorbing all of this; so any info, at any time is good info for me.

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