Help quick- Overshot my shock level

[Johnny B]

10/20/11- anticipate closing on 10/23/11
Water temperature 60F & next few days to get into the 40’s
pH 7.5 or 7.6;
FC 4.5-5 so shocked Target 18 by adding 554 oz bleach at 10:30pm
CC 0-.
TA 50,
Borates 25,
CH 220 so Target 300 & several hours ago I added 187oz by volume Calcium Chloride (Leslies Calcium Harness Plus).
CYA 60

Re-test FC 1 hour later at 11:30pm: FC 26 !

Want me to go add water to dilute it? Am I at risk at such a high FC?
How much water, 1 inch.

What did I do wrong? Pretty sure I got the Pool Calculator right but apparently not?

Thanks

 

[Ohm_Boy]

You'll be fine. According to the FC/CYA chart, shock target for CYA=60 is 24. The target shock level for Mustard algae is 34.

 

[Ohm_Boy]

As for the error, I'd place my bet on your pool being smaller than 19,800 gal.

 

[Johnny B]

I really appreciate your quick reply, it has saved me some work.
I was going by the pool calculator, not the chlorine /CYA chart.
If I had targeted 24 instead of 18, I ‘d be even higher now; yikes.
So I’m a bit confused still.

Did I misread the pool calculator?

My pool behaved super this season. The past few weeks it takes only 9-23 oz of bleach per day. Is that related to why the FC went so high in spite of reading the pool calc correctly.

Just trying to learn.

Thanks again

 

[Ohm_Boy]

I don't think you misread the calculator. If the pool gallonage is correct, and the bleach strength is correct, the amount you added should be about right for ~5 to reach ~18. I think I put in 19,800g, a current FC of 4 and A target of 18, and got 550oz or so, if I recall. So if the actual result in the pool is higher, then either the pool volume is less than 19.8k, or the bleach strength is higher than the percentage used in the calc, or you treated with more than the prescribed dose, ie., mis-measured the dose. There isn't much else. I'm still betting that the pool is smaller than 19.8k.

 

[Johnny B]

10/24/11; 8:30am, 3 days & 9 ½ hours after initial & only shock dose:

FC 12 (1 hour after the shock dose it was FC 26; I Targeted 18 so some error on my part)

Is it too early to close?
True, that the FC has fallen to about half of shock level”, however, I learned on the site here to: “wait until the FC drops back down to the proper “closing” level because High levels of chlorine and PolyQuat result in faster chlorine oxidation of the PolyQuat; this lowers the chlorine level and breaks up the PolyQuat into smaller pieces. These pieces can still be effective, but the loss in chlorine is wasteful. It's going to happen anyway, but at normal chlorine and PolyQuat levels it takes a lot longer (especially as the water gets colder). And high FC is a little harsh can lighten/bleach the mesh cover" (I think).

For me, my “closing FC” is halfway between a Shock level of FC 18 and a Normal level of 5-9 which is about FC 13.5 so obviously today's FC 12 is in that range. But I ask because:
- my Shock level last year was lower (due to a lower CYA)
- I don’t know the chemistry details re the specific FC related to “High levels of chlorine and PolyQuat result in faster chlorine oxidation of the PolyQuat; this lowers the chlorine level and breaks up the PolyQuat into smaller pieces. These pieces can still be effective…”;
- I don’t know the chemistry details re “high FC is a little harsh can lighten/bleach the mesh cover”.

My guess is that it’s fine to close, but so many time the pros’ comments have been a great help.

Is it too early to close?
Thanks

 

[chem geek]

Going from an FC of 26 ppm to 12 ppm over 3 days & 9 ½ hours is an average daily (24-hour) loss of 20% so that sounds about right at your CYA level and with some (but not intense summer) sunlight.

As for closing, you could add the Polyquat now and it will probably further lower the chlorine level and that's OK. Check the FC in a week after adding the Polyquat just to make sure there still is FC of at least 5 ppm or so. If there is, you're good to close. Even with an FC of 12 ppm, this isn't bad. It's keeping the FC up at a shock level and having it stay there over an entire winter that was the concern being expressed in the quotes you referred to.

As for being too early to close, I would base that more on the water temperature. You generally want to close as late as possible so that the water is cold -- below 50ºF would be good since algae growth would be far slower. You would then open as early as possible, when the water was still below 50ºF. That approach usually prevents any serious amount of algae from growing over the winter, even if the FC drops to zero. The loss of FC also slows down significantly at the colder temperatures assuming you are covering the pool to keep out most sunlight.

 

[Johnny B]

Thanks so much.
Water temperature is just under 60F & cooling so I’m fine but I hear what you say re 50F.
I’ll close today. I'll check FC in 1 week.
Thanks again for the help & good info.
I’ll report in the future if the cover lightened. I’m pretty sure it did last year a tad.

 

[Johnny B]

Chem Geek (or other)
Is my CSI etc ok.
Had a calcium scaling issue one winter because the pH got too high for too long. Didn't know I had to winter test. The following winter I tested. This is winter # 3 for me.

If you want me to do anything other than add bleach, please let me know.
Thank you


10/24/11- Polyquat & closed
57F

10/31/2011- 1 week after closing on 10/24/2011
55F
pH 7.4, undershot it a tad I suppose.
FC 3.5; ChemGeek said above that I want an “FC of at least 5 ppm or so” so I'm going toTarget FC 6 by adding 97oz bleach Water is about 18,654 gallons now for the winter
CH Assume is 300 based on the 10/20/11 Tteatment to target 300
TA assume still 50, will test next time
CYA assume still 60
Borates assume still 25
CSI -0.75

 

[chem geek]

Is there any particular reason your TA is so low? I wouldn't close the pool with a CSI as low as yours. Unless you were having a lot of trouble with pH rising, I'd raise the TA, perhaps to 70 or 80 ppm, and target a somewhat higher pH of around 7.6 to 7.7 unless you've got a high risk of metal staining (i.e. lots of metals in the water). Even if your pH went to 8.2 over the winter with 80 ppm TA, the CSI of +0.30 would probably not lead to scaling. In the past, I presume your CH and/or TA was higher and that along with high pH led to scaling.

 

[Johnny B]

TA is at 50 because we (Jason, you, me, etc ) decided that was ok. It was TA 50 all summer & the pool behaved the best ever with respect to pH, & pretty much everything. I don’t have a metal “staining”, issue, a small rust/exposed rebar issue that doesn’t worry me unless it worries you (I’ll fix at the next re-plaster in a few years, a rising iron level I suppose). I will go & raise the pH to 7.6 (historically it rises, I’ll re-test in 21 days unless you want it sooner, getting colder) & I’ll raise the TA to 70 unless you want TA 80, just let me know. If we want a TA of 50 next summer, I can get it there, I’ll ask you guys then.

Looks like 70 oz of baking soda will treat both the pH & the TA to reach the above pH 7.6 & TA 70 targets ( I wouldn't add the 14oz & 70oz by volume would I?)

I really appreciate your help. Let me know

 

[chem geek]

I think that 70 ppm TA with 7.6 pH is a reasonable compromise and yes, you can just check the pH in a few weeks since it probably won't rise that fast. Colder water doesn't outgas carbon dioxide as quickly so shouldn't rise in pH as fast. Also, if you cover the pool, that will cut down on outgassing considerably.

 

[Johnny B]

update:

11/20/2011 (3 weeks since last test on 10/31/11, 4 weeks after closing on 10/24/2011)

Temperature 52F
pH 7.7 so dropped to 7.6 by adding add 8 oz acid ( calc said 9 oz but I went w 8 oz)
FC 4.5 so Target 6 & added 77 oz bleach
TA 75

My next test will be in a month on 12/20/2011

Let me know if you like as is, or if want a change.

Thanks as always

 

[chem geek]

It's fine where it is. Don't forget that pH will naturally rise as the temperature drops anyway so it tends to keep the saturation index from changing very much. So having a higher pH as the water gets colder is not a problem unless you've got very high metal content. So letting it get to 7.7 or 7.8 is not at all problematic.

 

[Johnny B]

Geeze, now I overshot my pH; winter testing is a challenge, cover on, sump pump only, etc.

12/23/2011; 33 days since last test & treatment; about 8 weeks after closing
Temperature 48F; it has been an unusually hot Dec., expect Jan & Feb to be their typical cold.
pH > 8.2 so assume 8.3, Target 7.6 with 65oz acid
FC/OTO 1.5, Target 6 with 174oz bleach
TA 75
Assume CYA 60 & Borates 25 & CH 300
CSI: -0.38

pH re-test 6 hours after sump pump circulation: pH 7.2 & CSI now -0.74; I’m not worried unless you guys are & want me to alter the pH now; the pH historically rises & did so quite a bit in the prior 33 days; hard to believe the pH won’t be 7.5 14 days hence. I can leave the sump pump circulate if you want me to, if so then how many more hours or days?
Thanks

 

[Ohm_Boy]

There's absolutely nothing wrong with a pH of 7.2. Just let it ride.