"how to shock" article update suggestion

[reebok]

I'd like to recommend chem geek's 3 criteria for knowing you're done shocking be added to the how to shock article in pool school. I would also like to recommend, if he's ok with it, changing sparkly to clear, because I don't think my water sparkles per se. maybe it's the bird cage, I dunno, but I'm not the only one. cant-get-water-to-sparkle-t14422.html
my reason for suggesting this (besides the fact it's repeated 100 times a day, sometimes to the same individual ) is that some people fall through the cracks (example: can-t-seem-to-get-ahead-of-this-algae-t13033.html), and not everyone posts here, they simply follow pool school without having to ask for individualized help.

 

[frustratedpoolmom]

Great suggestion.

 

[JasonLion]

There is a disagreement about the three criteria. I don't think that clear water has anything to do with it, as long as the overnight FC loss test is being done correctly. The Pool School article does cover the other two criteria.

The value of the water is clear (and possibly sparkly) criteria is when you are fighting algae and don't have a FAS-DPD chlorine test. So in many ways it comes down to trusting people to do the overnight FC loss test correctly, or adding a third criteria, which wastes chlorine for a lot of people, to cover others who fail to follow the directions correctly.

I wonder if there is a third way of phrasing things that doesn't have either of the problems that the two current approaches have.

 

[duraleigh]

I don't think that clear water has anything to do with it, as long as the overnight FC loss test is being done correctly.

Why the heck would we tell anyone to do the overnight FC test (or test for CC's) when their water is the color of their lawn??

 

[JasonLion]

When you are shocking, and the overnight FC loss test shows no FC lost, then what does it matter if the water is still murky? The algae is all dead, and you are just waiting for the filter to do it's job. During the period while the filter is working, you can go back to normal FC levels.

The challenge is when people do the overnight FC test incorrectly. The most common one is people with a DPD test saying that FC was 5 in the evening and was still 5 the next morning. The DPD tests max out at 5, so the actual level could well be higher and could well have fallen by more than 1.0 overnight and yet still read 5 on the test.

One way to deal with that is to tell them to wait for clear water. Now the DPD test people will stay at shock level longer. But that forces people who are doing the overnight FC test correctly, with a FAS-DPD test, to spend several additional days at shock level, wasting a significant amount of chlorine, while they wait for the filter.

So, the question is, can the criteria be phrased a different way so that it doesn't have either of those problems.

 

[Guest]

I don't think that clear water has anything to do with it, as long as the overnight FC loss test is being done correctly.

Why the heck would we tell anyone to do the overnight FC test (or test for CC's) when their water is the color of their lawn??

Good point and one that often seems to be overlooked. It would be more prudent to tell people to shock until the water is no longer green and there are no CCs and THEN tell them to check for overnight FC loss if you think it's needed.

 

[frustratedpoolmom]

What about this:

You are done shocking when:

You experience a FC loss of 1ppm or less overnight, using the FAS-DPD test described here (link to the OFCLT article)
and your CC is .5 or less.

Note: If you do not have the FAS-DPD chlorine test, you should continue shocking your pool until your water is clear.

IDK...just a thought.

 

[reebok]

Note: If you do not have the FAS-DPD chlorine test, you should continue shocking your pool until your water is clear.

even better:
Note: If you do not have the FAS-DPD chlorine test, get used to your algae and stop wasting everyone's time. :gone: :tongue:

anyway, I guess I opened a can of worms. thanks Jason for clarifying that the overnight loss test is absolutely definitive. I thought it wasn't because of the thread I linked above about the guy who had the algae come back. I replied to him to try to get some more info and hopefully help him get cleared up.

 

[Guest]

The challenge is when people do the overnight FC test incorrectly. The most common one is people with a DPD test saying that FC was 5 in the evening and was still 5 the next morning. The DPD tests max out at 5, so the actual level could well be higher and could well have fallen by more than 1.0 overnight and yet still read 5 on the test.
Then teach them to do the dilutions such as the instructions in the Taylor K-2005 have right on the lid. Yes, I know that there will be a loss of precision but that does not mean that someone cannot tell if they are maintaining their FC at a shock level that will do the job. Just don't keep it at the minimun shock level.
One way to deal with that is to tell them to wait for clear water. Now the DPD test people will stay at shock level longer. But that forces people who are doing the overnight FC test correctly, with a FAS-DPD test, to spend several additional days at shock level, wasting a significant amount of chlorine, while they wait for the filter.
Reread that and tell me where it makes sense in light of my first reply in this post.
So, the question is, can the criteria be phrased a different way so that it doesn't have either of those problems.

Yes. Just add a 'safety margin' to the shock level and have them keep it at shock level until there is NO cc. Those of you who were active on PF before this site ever existed KNOW that we helped clear plenty of green pools when people only had an OTO test kit from walmart and they were doing dilutions. I know YOU remember this, Dave. While an FAS-DPD test certainly makes things easier by a factor of several hundred per cent it CAN be done with simpler tools and has been countless times. It might use a few extra gallons of bleach but it certainly can be done.
(I know that this is not a popular opinion on here and I am sure that I will hear about it but can anyone say it is NOT true?)

 

[JasonLion]

I don't disagree about the OTO test at all, but as you said: "FAS-DPD test certainly makes things easier by a factor of several hundred per cent". The more you talk about OTO, or DPD, the more people miss out on the fundamental point, which is how much better FAS-DPD really is.

Perhaps that is the correct way to approach it, more or less like what frustratedpoolmom said, put a tidbit of why FAS-DPD is better into the shocking article. Something like:

Continue shocking until:

• CC is 0.5 or lower;[/*:m:32foe5oi]
• the overnight FC loss test shows a loss of 1.0 ppm of FC or less;[/*:m:32foe5oi]
• and, if you don't have a FAS-DPD test, continue shocking until the water is clear (which uses more chlorine).[/*:m:32foe5oi]

Or something to that effect anyway.

 

[Guest]

which comes full circle to how it was done at PF. Just because someone only has an OTO test at their disposal does not mean that they should wait until their new testkit arrives before they start shocking.

 

[chem geek]

There are times when one could have the water still show algae and not register much of an overnight FC drop nor much CC. This usually occurs when there is some, but not a lot, of mustard/yellow algae. I agree that initially for the most common problems with green algae where the pool is visibly green or cloudy that it's pretty obvious one should remain at shock level until things clear up and there really isn't much point wasting reagents doing testing. At the point when the pool gets fairly clear, a lot of people stop too early and that's when testing for the overnight FC drop and CC level becomes important. The other scenario for these latter tests is when the pool is clear but has a chlorine demand as often happens during early nascent algae growth or when there is ammonia (or other similar CYA degradation byproducts) in the water when opening a pool (or otherwise having the FC get to zero).

So I think the proper sequence is 1) shock when the water isn't clear (i.e. keep shocking until it's clear, but see #2, #3), 2) even when the water is clear, if the FC drop overnight is > 1 ppm then keep shocking, 3) even if #1 and #2 are true but you have CC > 0.5 ppm then keep shocking.

The only caveat to the above would be if water clarity was affected by other issues such as over-saturation with calcium carbonate (i.e. saturation index too high) or poor filtration or circulation. Also, the 1 ppm rule for FC drop can be loosened up a bit if the shock level is quite high -- well above 20 ppm FC, for example. If one saw a 2 ppm FC drop overnight but was shocking at 30 or 40 ppm FC (say, for mustard/yellow algae shocking), I wouldn't sweat it if the other criteria were met. Since this is rather rare, I don't think it needs to be part of the primary criteria.

Richard

 

[JasonLion]

With my filter, an ancient partially broken undersized sand filter, it can easily be a week for the water to clear up after the algae is completely dead. For some people with Intex cartridge filters, it can be two or three or four weeks for the water to clear up after the algae is completely dead. We run into this kind of situation fairly regularly, undersized sand filters and Intex cartridge filters are both relatively common.

For everyday green algae, it frequently only takes one, two, or three days of shocking to wipe it out. There isn't any point in maintaining shock level for the extra week or two while the filter is working, as long as you know that the algae is dead. Maintaining shock level the entire time would take three to eight times as much chlorine, or more for some Intex owners, which becomes a significant expense and is much more work.

An oversized DE filter, or even an oversized cartridge filter, will clear up the water far more quickly after the algae is dead. In that situation clear water can be a much more useful indication. You don't have the huge lag between algae dead and clear water that a small sand or Intex filter imposes.

With mustard algae, you can have totally clear water, 0 FC loss, 0 CC, and no visible sign of algae at all, yet the mustard algae can come back within a few days of the FC level getting back to normal levels. The shocking criteria, even the more conservative versions, are no help at all against true mustard algae.

With ammonia, the water is clear the entire time, so you are depending on CC levels, and in the final stages overnight FC loss, as the indicators.

With fairly tough algae that has formed a robust biofilm, the water can be mostly clear, once in a while completely clear, long before you burn through the biofilm. This is most common with low phosphate levels, when the algae doesn't take over the pool but rather grows slowly on the walls. In this situation you often see the algae on the walls, but occasionally it hides somewhere (light niche, bottom of stairs, etc) and overnight FC loss is the only indication that tells you what is happening.

 

[chem geek]

Jason,

I get your points, but what are you suggesting? That they shock until the overnight FC loss and CC criteria are met and not to worry about cloudiness (unless they can't see the floor drain well, which would be unsafe)?

You bring up a good point about the weak Intex pumps and filters. Also, there is no floor drain and the circulation is poor. If they have the ability to vacuum-to-waste, then if the pool does not clear should a floc be recommended? Though a last resort, when circulation is very poor there may not be much else that can be done if there isn't sufficient patience.

Richard

 

[JasonLion]

I am suggesting that clear water not be a criteria for being done shocking if you have a FAS-DPD test kit and are doing overnight FC loss tests. With a FAS-DPD test, an overnight FC loss of 1 or lower should be good enough to return to normal chlorine levels, even if the filter hasn't caught up and cleared the water yet.

Letting the FC level fall back to normal once the overnight FC loss is 1.0 or lower, even if the water is still cloudy/murky, works fairly well in practice. The most common problem with this approach is people who use a less precise chlorine test (OTO or DPD) and stop shocking way too soon because their test kit can not detect that they are actually losing FC overnight. That mistake comes up often enough to be troubling.

The current wording in Pool School is unfortunate. It says

until the FC level remains the same overnight and CC is 0.5 or lower

and only mentions FAS-DPD in passing in a different paragraph. There are a couple of ways to fix this. One, is to use "the water is clear" as a third criteria. Another is to stress that the FAS-DPD test must be used for the existing approach to work. A third would be to explain two different approaches to knowing when you are done shocking, one for FAS-DPD users and a different one for everyone else.

This topic got started because someone noticed that different criteria are being given for when shocking is complete by different people and in different parts of TPF. They thought that the Pool School version should be updated to match the one most commonly stated in posts, which is to add clear water as a third criteria. At this point I am advocating for adding clear water as a criteria only when you do not have a FAS-DPD chlorine test. Whatever happens, the Pool School shocking article needs to be updated, since the current wording isn't really supported by anyone and has been causing problems.

---

I hadn't thought about the especially bad circulation possibility. In pools with no main drain, a fairly deep deep end, and a poor circulation pattern, it is possible for chlorine to not mix down to the bottom of the deep end at all well. As a result, you sometimes get into a situation where the upper say four feet of water are clean and properly sanitized but the deep water still has algae. In that situation, I would imagine that FC levels would fall by more than 1 overnight, but I don't have any experience with this combination so I don't know for sure what will happen.