Breakpoint Chlorination

[chem geek]

First regarding the book that talks about forming monochloramines to help kill the algae, well this is true that you'd be forming a LOT of monochloramines with that method. But you WON'T achieve breakpoint chlorination without adding a lot more chlorine (unless I screwed up in my calculations).

As for BleachCalc, yes it is "technically" wrong, but as you can tell it's not wrong by much and the error in measuring cups plus the degradation of chlorine over time means that you probably do need to use a little more to end up with what you expect. WHOOPS! This means the error in BleachCalc is in the wrong direction! BleachCalc probably has you add even less than you need rather than more.

Also, the density of the 12.5% liquid chlorine being 1.16 g/ml is not true for bleach which is probably closer to water density, probably around 1.07 g/ml, so BleachCalc would be even a little more "too high" in this case (that is, reporting that the change in ppm is more than it really is). I have verified my calculations with my own pool and the use of 12.5% chlorine to the extent possible, but this isn't easy since I do suspect that the chlorine does degrade somewhat at the pool store.

Mmmmm. I think we need to verify this with some more real-world experience before we get Michael to change BleachCalc. What is your experience?

Richard

[waterbear]

My experience with BleachCalc and chlorine is zero. I have never needed to add bleach to my pool with the SWG. Never had any any CC to speak of!

[chem geek]

My experience with BleachCalc and chlorine is zero. I have never needed to add bleach to my pool with the SWG. Never had any any CC to speak of!

Oh yeah, I forgot. Rub it in, why don't you! One of these days I'll join the SWG club...one of these days...

[waterbear]

Just stating the facts....I had my nephew, his wife and their three kids staying with me this week (they left yesterday) and I checked the pool once during the week (Wednesday) after a day of heavy use and there was still no CC. (I didn't check the water until I got home from work at 1 am and the pump does run for 3 hours in the evening but it seems that was enough to take care of any that might have formed. I also suspect that my 3.5 year old grand nephew might have 'gone number one' in the pool that afternoon from an overheard converstaion between him and his mother in the pool while I was geting ready to go to work....that's why I checked it that evening!

[chem geek]

The consensus so far on this thread seems to be that people manually dosing chlorine shock from zero to 3 times per season -- most only once or twice. So assuming some of them also have kids with, well, #1 releases, my guess that a regular manual dosing of chlorine is pretty similar to what an SWG does may be correct. It's obviously not as good since even once or twice a day chlorine addition isn't the same as several hours each day, but it does show that, as CarlD says, "Stay ahead of your water!" really works.

Richard

[KurtV]

That small error in the BleachCalc alogorithm may explain why the Best Guess Table seems to sometimes understate the chlorine needs for reaching "shock levels". Some people may not actually ever be getting to the breakpoint if they're dosing based on BleachCalc. Or would that be overstating the effect?

I certainly don't want to sound ungrateful for Michaels fine software. It has made the pool maintenance part of my life much simpler on many occasions.

[chem geek]

I don't think it is BleachCalc that is the root cause of any underestimation of how much chlorine is needed to shock, though you are correct that if I am right about the error, then it will underestimate how much to add. I believe the much bigger potential problem (that we don't know for certain yet) is that Ben's table tracks reasonably well with the ppm HOCl theory for his "min" and "max" columns, but not well at all for the "shock" column. Look at my FC.htm chart and you can see that (ignoring very low CYA since the required FC is so low as to be impractical to maintain) the 0.02 ppm column roughly correlates to Ben's "min" while the 0.05 ppm roughly corrleates to Ben's "max", but there is no good correlation for his "shock" column. We don't know which way the error is, if any, but if I were to hazard a guess, I would say that the proper "shock" level is at around 0.5 ppm though possibly 0.2 ppm *might* do the trick in some cases. If 0.5 ppm is correct to kill algae, then the high CYA levels in Ben's chart underestimate the amount of chlorine truly needed.

Only real-world experience will tell what we should do to go forward -- if the ppm HOCl is valid for the shock to kill algae and if so, what level is appropriate.

Richard