Higher chlorine loss than last year

[dancu]

In the morning FC 20.5 8am s
Last night 9.5 7 pm
This morning 8.5 7am lost 1ppm overnight
Good enough or do I have to bring it back up to 20ppm ? ,slime is gone...

[chem geek]

Personally, I'd play it safe and keep it at shock level another 24 hours. A 1 ppm drop overnight is not huge going from 9.5, but it may indicate something is still getting killed or broken down even if it's not visible. Better safe than sorry.

[dancu]

Didn't play it safe and now I am sorry...3.5ppm at 5.30pm....
Back to shock level tonight...seems like an a large drop compared to overnight
even with the added uv.

[dancu]

6/24 pm 3.5 ppm, added bleach to 25ppm(9 jugs supposed to be 18.9 ppm,did I test to soon at 2 hrs?)
6/25 am 23.5ppm
6/25 pm 13ppm, added bleach to 25 ppm(4 jugs are supposed to be 8.4ppm but I tested a 12 ppm increase after 2hrs)
6/26 am 24 ppm
6/26 pm 12 ppm
6/27 am 11.5ppm
6/27 pm 5.5ppm
losing 6 ppm during the day, yes it was hot and sunny but I am in northern new jersey.....Any suggestions to bring this down?

[chem geek]

Other than using a cover, I'm not sure what to suggest. You are already at 60 ppm CYA. A 6 ppm loss out of 11.5 ppm is about half and given that you only lost 0.5 ppm at night it would appear that this loss is due to sunlight. This is the peak time of year and even in northern latitudes the amount of solar radiation is quite high. The difference in northern latitudes is that this situation doesn't last very long.

I used to think that operating at a lower CYA level would save you chlorine. So running at 30 ppm CYA you would go from 7 to 3.5 ppm FC and only use 3.5 per day which is less. But now we have reports and experiments (in this thread) of CYA saving more chlorine even at the proportionately higher CYA levels. So that would say going to 80 ppm CYA or higher might help (the effect is non-linear) even maintaining the higher FC level. So I'm stumped and until we get a lot more data on true CYA protection of chlorine, I don't know what to say.

[dancu]

I am starting to think that a cya of 60 is a bad place to be because using Ben's
chart it puts me at the bottom value that requires 5 to 10 ppm cl
Could you help me out with the testing method?
Testing at 7pm with my back to the sun I test 60-65 cya
At 2pm back to the sun 55-60ppm, and if I face the sun I can squeeze out 45 -50 ppm.
Can I use lower scale of 3-6 ppm?
That would probably save me half....

[chem geek]

You are probably in the 60 ppm CYA range given what you described for testing. It's a hard test to get right and it has error of +/- 10 anyway. The minimum amount of Free Chlorine at that CYA level is 4.5 ppm (equivalent to the "Min" in Ben's chart) while a reasonable target (equivalent to a mid-point in Ben's chart) is 7 ppm. If you want to just make sure you never go below around 5 ppm, that would be OK, but this won't save you a lot.

It's really too bad it's not easier to change CYA levels since you could just try a lower level and a higher level to see if it made any difference (with corresponding lower and higher FC levels). You could take a large basin or bucket of pool water, dilute it with tap water to reduce CYA level and try that (adjusting FC level as needed). Then take your pool water in another basin (or the same one the next day) and add a little CYA to it and chlorine and see how the FC level holds up. It's not a perfect experiment because the depth of the basin or bucket isn't the same as your pool, but it's better than nothing.

Richard

[brent.roberts]

Question: when is the last time you cleaned out your filter.

Maybe there is a lot of junk in there that you can't see that is consuming some
of the chlorine.

Put a cover on to stop the sunlight loss. You're going to burn up the cost of a cover in extra chlorine. Even in NJ the sun is very high this time of year and the UV loss can be huge.

[dancu]

Oh, I like that idea!
Pool is 3 years old, sand filter never never got cleaned or replaced only backwashed
Drop in cl overnight while at shock levels with the filter running all night was minimal though...
Just thought about the light niches,what or the odds something is growing in there, or am I losing it now......

[brent.roberts]

If you got no significant drop in chlorine overnight, then I don't think gunk in the filter is the issue. From what I have seen in weather patterns most of NE USA and our area in Canada (Toronto) has had much greater than normal amounts of sunlight. We only got 1/4" of rain in June and normally get 2 1/2", so UV action on the chlorine will be much higher than normal. Maybe just carry on and see if it goes back to normal for you when we get more normal weather.

By the way, despite what some pool stores tell you, filter sand almost never needs replacing.

Good luck