adjust cya before or after shocking

[PoolDoc]

Question for Aylad--why are the chlorine amounts you said are needed to shock different than what I calculated with the Pool Calculator?

I'll answer that:

(1) The Poolcalculator is NOT ours, but it is based on Chem_Geek's chlorine spreadsheet, which laid out the analytical basis for my Best Guess chart, which was partly analytical, but partly based on my field experience.
(2) Both the calculator, and Chem_Geek's spreadsheet attempt to be EXACT. We don't, and not by accident. Pool volume calculations, test kit errors, and dosing errors all come together to make the sort of exactness suggested by those tools, unreachable in practice.
(3) So . . . we try to give estimated doses, that are calibrated to avoid problems. In practice, this means we estimate CHLORINE doses HIGH, and everything else LOW.

What Janet did was give you a dose for 15 ppm MORE chlorine -- in practice, that's the right thing to do, since she didn't know how much chlorine you'd have in your pool, when you added your dose. But, when you used the pool calculator, you probably took the chlorine level from your LAST test -- even though that value was unlikely to be correct by the time you added more chlorine -- and entered that into the calculator. So, the calculator told you how much MORE chlorine you should add to get there.

Mathematically, that's correct. But, practically that's wrong.

Richard (Chem_Geek) doesn't agree with me on this point. But, I think that's partly personal error. Richard is EXTREMELY careful and meticulous in his personal habits, and tends to assume others will be, too. He recently told me he'd NEVER had even a drip when using muriatic acid, as we discussed how we should tell people to add acid to pools. If anyone else had told me that, I'd assume they were exaggerating or outright lying. But, I'm pretty confident that he may be the only pool person who is that precise.

So, the pool calculator and his spread sheet work out for HIM, as exactly as they imply. Of course, if there's another pool owner in the USA as exacting and precise as he is, I'd be surprised.

My view is that the pool calculator is more exact in theory (apart from a few errors it has embedded), our approach is more correct in actual practice.

[Kateyru]

Thank you so much for taking the time to explain that. Makes perfect sense!

I kinda screwed up as I ran out of titrating reagent this morning BEFORE I could test. Should have been paying attention to that... I ran to the store and got distilled water to test that way. My best guesstimate using distilled water testing is that FC is at least 15. I actually did test FC before I added bleach last night so I could be fairly accurate with Pool Calculator calculations but then ended up adding a total of 5.5 gallons of 6% because that's what Janet said to do (and now I understand why). So, last night, FC should have been at about 21.5. All that to say that I think FC is at least 15 now. So, should I add more bleach now for insurance? If so, how much? Should I be testing pH when I test FC?
Thanks!!!

[aylad]

Leave the pH alone and don't worry about it. With the chlorine level that high, the pH result won't be accurate anyway, but if you're just using bleach, the pH is not going to change enough to be an issue. Focus on your chlorine and forget about the rest for awhile.

If you "add more bleach for insurance", then you may just be wasting bleach, so I wouldn't do that. Test your water again, estimate the level, then add bleach if you're under the 15 ppm mark. (And if you did get to 21 ppm last night, it won't hurt the pool--it would just be more available chlorine to work on the algae).

[Kateyru]

Ignore previous post as I think I am muddling through. Here's another related question. I reviewed the thread about my previous efforts to get rid of algae. Quick recap: in process of shocking, and after turning off SWG, FC test results were:

4/11/12, 5PM, FC =15.5
4/12/12, 6AM, FC =14
4/13/12, 7AM, FC =10
4/13/12, PM, FC = 8
4/14/12, AM, FC = 7
4/14/12, PM, FC = 7
4/15/12, AM, FC = 7
4/15/12, PM, FC = 4.5
4/16/12, PM, FC = 7.5
4/17/12, PM, FC = 9.5
4/18/12, PM, FC = 8
4/19/12, FC = 10.5
4/20/12, PM, FC = 8.5
4/21/12 PM, FC = 7
4/22/12, PM, FC = 4.5 (I turned SWG back on at this point)
4/23/12, PM, FC = 5 (I added 48 oz. of CYA, don't know if I added bleach)
4/25/12, PM, FC = 11.5 LEFT TOWN
5/4/12, PM, FC =10
5/5/12, PM, FC =9 (added 48 oz. of CYA)
5/6/12, Am, FC = 8
5/7/12, AM, FC = 6.5
5/7/12, PM, FC = 6
5/8/12 I"VE GOT ALGAE FOR SURE!
5/8/12, PM, FC = 6.5 and shocking starts

Also, re: test results, just fyi, when tested during shock period, CC was always .05, < .05, or 0.

As I said in previous post, it is clear to me now that I didn't keep FC > 15 long enough.
So, here's my thought/question:

**** Can algae, over time, raise its tolerance to FC? That is to say, if you don't get all the algae when you shock (due to human error or whatever), at some point in time after repeated unsuccessful attempts to shock, will the FC need to be maintained > 3 - 5 ppm in the future to keep algae at bay? I am not a chemist (obviously) and have never had much interest in chemistry but am somewhat fascinated by all of this.
An aside, it seems like there could be some really interesting science projects out of pool water study. I'll have to remember that when my grands are a little older

[Kateyru]

Janet, we were posting at the same time. I remembered (in the middle of the night) that testing pH was moot point when shocking. I've been testing as best I can (as you suggest) and brushing.
You can see from my previous post, that I am not only focused on the chlorine, I am somewhat obsessing...

[aylad]

Once you get the algae killed off, you're going to need to raise your CYA levels to help protect your chlorine from the sun. When that happens, you're going to have to raise your chlorine levels to compensate for that. Look through this thread for some of the sigs that have the link for the "best guess chlorine chart", and that should answer your questions regarding higher chlorine levels.

In looking at your chlorine log, you simply did not sustain the chlorine levels long enough to kill the algae. As we've said many times throughout this thread, you need to get it to the 15 ppm make and keep it there until the algae is dead. By letting the chlorine levels yo-yo up and down like that, you may be preventing further algae growth, but you're not doing anything to kill the original bloom.

I don't really rely on CC readings for algae determination....sunlight and chlorine both help eliminate CC. I have personally seen algae on the side of my pool with a CC of zero. That's why a much more reliable test is to see no chlorine consumption overnight.

[Kateyru]

I was actually in the process of raising CYA level when the algae made itself known (to me) so I'm clear with that.
I do think I understand most of this now. In my previous shock attack, somehow the focus and comments back and forth got on FC loss from evening till morning coupled with minimal CC. The length of time my FC was at or above 15 ppm seems to have gotten overlooked it.
Many thanks again!

[BigDave]

**** Can algae, over time, raise its tolerance to FC? That is to say, if you don't get all the algae when you shock (due to human error or whatever), at some point in time after repeated unsuccessful attempts to shock, will the FC need to be maintained > 3 - 5 ppm in the future to keep algae at bay?

I don't know if algae can become more cl tolerant through selection, makes some sense that you may be cultivating a cl resistant algea population. I do know that once you've raised the FC high enough for long enough to kill that population, you won't have to be concerned raising your base cl level for the resistant population as it will be gone. Any new algea that enters the pool will not have been through the selction process and will be no more cl tolerant than all the other algae.

[Kateyru]

Touching base again. I started my 2nd shock attack on 5/8 after messing up the first time, i.e., I didn't keep FC > 15 ppm long enough to kill all the algae. About the time I started 2nd attack, I ran out of reagent so used dilution testing until new reagent arrived. Using dilution testing then FC testing with K-2006 kit when replacement reagent arrived, I've tried to keep FC at or above 15. So, this is day 12. I was out of town for a couple of days this past week and am aware that FC got below 15 a couple of times. How much of a setback is that? I didn't lose any FC from last night until this morning. My plan, per forum guidance, is to stay at or above 15 for an extra day, that is, 1 full day after no chlorine loss overnight. That would be today if the 2 recent dips below 15 don't have a significant effect overall. Guidance please.
Thanks!

[Watermom]

You are right to give it the extra day as long as there is still no more than a 1ppm chlorine loss overnight from sundown to sunup and you don't have a CC reading.