Disappearing CYA

[waterbear]

Not much difference in a Taylor K-2005 and a Taylor K-2006, I can measure high levels of chlorine by halving the pool's water and multiplying the reading by 2 or if higher 1/3 and x3.

Please let me know if what I said makes sense.

Thanks!

Actually, there is a HUGE difference in DPD and FAS-DPD testing. First, it has been found that about 4 out of 5 men have difficulty in differentiating the red colors on a DPD test (women do not have this problem) and second, dilution decreases your precision on the test so the FAS-DPD test is much more precise (down to .2 ppm!) compated to doing dilutions with the DPD test. The K-2005 does include dilution marks on the tester for 1:1 dilitions (multiply results by 2) and 1:4 dilutions (multiply results by 5) but these are only really going to give you more of a ballpark figure while the K-2006 will give you results that are precise to either .2 or .5 ppm depending on the size of your testing sample. (I have both kits, among others).

Also, FAS-DPD testing directly measures CC instead of measuring TC and then having to subtract the FC from the reading.

[vinnygnj]

mbar,

I guess I actually didn't ask any questions, I was just thinking out loud. I don't have a very big outbreak of algea and luckily my pool didn't get away from me.

If my chlorine didn't disappear to 0 or very low, hasn't the algea been killed? When you were fighting the algea battle where you losing only a small amount of chlorine at night or most of it? I have fought with it and have had no chlorine by morning - that's why I ask.

Since the chlorine didn't go below 3 and my stabilizer is probably around 35, isn't all my chlorine above 3 killing anything it can? I put enough chlorine to last a night and a day of sunshine.

I know of 2 reasons for shocking a pool 1) breakpoint chlorination which I know isn't practiced here and 2) put enough chlorine into the water to kill the organisms and make sure there is enough chlorine left over so that you're assured a kill (and yes it might take days to accomplish that kill if chlorine gets too low). Why go to 15? Is there something else I'm missing?

waterbear,

I understand the color thing and yes at times I can't tell the difference between 1, 1.5 or 2. But I usually can tell the difference between 2, 3 and 5. Maybe other men can't and maybe as I get older I will lose this ability so I will have to go to the K-2006.

As far as the precision of the testing, why do you need to be that precise?

I know that that as CYA rises you need to add more chlorine but is there really a difference between 5 PPM and 5.5 PPM at a CYA of 30 or 100. I would think that if you were close to a important level that you just add more chlorine for a safe measure. If I almost halved the water and I almost got to a reading of 3, well I'm about 6 - I don't see a problem unless you wanted to precisely add enough chlorine for breakpoint chlorination but like I said - add more than just enough.

With CC, I thought that the only time you test it is when you lose large amounts of chlorine and you need to break the CC before it starts smelling? I was under the impression that the belief here is that sunlight destroys the CC. I typically don't test for CC in the pool after Ben stated that and whenever I have I had none.

[mbar]

Owww, my head hurts I will leave this to the chemistry pros, like waterbear and chemgeek. All I know is that whenever I lose chlorine overnight, it is because it is fighting something. If you lose a few ppms it is ok when the water starts at shock. I just think you are asking for trouble when you are playing around with such small numbers as 1ppm to 3ppms to do the work. Just as you said, it is not precise, therefore I would take it to shock and keep it there until the chlorine seems to be holding. You can tell with your own pool, as everyone's pool is different. So you can do as you like, but why are you so adverse about shocking the pool? If you are just after the reasons why shocking is needed, then I will leave it to the chemistry pros

[vinnygnj]

Didn't mean to make your head hurt!

I like knowing the reasons to things.

[waterbear]

Since the chlorine didn't go below 3 and my stabilizer is probably around 35, isn't all my chlorine above 3 killing anything it can? I put enough chlorine to last a night and a day of sunshine.
Algae is harder to kill than bacteria and 3 ppm FC is the MINIMUN for a CYA above 30 ppm (but less than 50 ppm). It often takes a higher level to keep algae at bay.
I know of 2 reasons for shocking a pool 1) breakpoint chlorination which I know isn't practiced here and 2) put enough chlorine into the water to kill the organisms and make sure there is enough chlorine left over so that you're assured a kill (and yes it might take days to accomplish that kill if chlorine gets too low). Why go to 15? Is there something else I'm missing?
I don't know why you have the impression that breakpoint chlorination is not practiced here. Breakpoint means adding enough chlorine to destroy any CC in the water. The formual for breakpoint (10x the CC level) does not always hold true and that is what is usually said but the actual process of reaching breakpoint is what is talked about when people are told to shock to destroy CC.
waterbear,

I understand the color thing and yes at times I can't tell the difference between 1, 1.5 or 2. But I usually can tell the difference between 2, 3 and 5. Maybe other men can't and maybe as I get older I will lose this ability so I will have to go to the K-2006.

As far as the precision of the testing, why do you need to be that precise?
Well, since it's usually recommened to 'shock' when the CC is greater than .5 ppm and you yourself said that you cannot differentiate tha small an increment with the DPD test I think that answers your question.
I know that that as CYA rises you need to add more chlorine but is there really a difference between 5 PPM and 5.5 PPM at a CYA of 30 or 100.
At a CYA of 100, no. At a CYA of 30, possibly.


With CC, I thought that the only time you test it is when you lose large amounts of chlorine and you need to break the CC before it starts smelling? I was under the impression that the belief here is that sunlight destroys the CC. I typically don't test for CC in the pool after Ben stated that and whenever I have I had none.

According to the precision of your testing which you have stated is 1 ppm or greater!

[vinnygnj]

I understand the concept of breakpoint chlorination, I could swear that I read a post by Ben a few years ago that he didn't beieve in the process of breakpoint chlorination, he made mention of CC will be broken down by sunlight - I guess I'm mistaken.

The K-2005 kit has an increment at 0.5 PPM and I can see that. I did check for CC when my chlorine was 0 and had none. I stopped checking my CC based on the above info. I do throw in 2x the normal chlorine at times to kill anything that hasn't been killed. I should have checked that my CYA was still there and probably should have shocked the heck out of the pool in the beginning of the season.

It definately is a learning experience.

[waterbear]

The comparator in the K-2005 is calibrated at .5, 1, 1.5, 2, 3, and 5 so while it can determine .5 CC at lower chlorine levels it's precision is only 1 or 2 ppm at the levels most likely encounted in pools with normal CYA levels (3.5 ppm FC and 30-50 ppm CYA). Dilutions will further decrease the precision of the test. This is why FAS-DPD testing is better. The precision is either .5 ppm or .2 ppm (depending on sample size) no matter what the FC level is.

I wonder if this is the thread you are referring to when Ben said he wished people would not test CC? I think the point he was trying to make was that people worry too much about small amounts of CC spikes when they should be worrying about general water maintenance. UV will destroy these small amounts of CC but if there is a large amount caused by some chlorine demand then high chlorine levels are needed.

Here and Here are artricles by the PPOA about superchlorination which basically say the same thing Ben said in the thread above and have some veryi interesting info.

[vinnygnj]

That probably is the post and I understand that small amounts need not be burned off with chlorine but I would also think that adding 6 PPM FC to a pool with 0.5 PPM CC will burn it off assuming that the CYA is at a low level.

As I said I never test for CC in the pool, only my spa but I guess in a situation like what I'm going through it might be worthwhile to test. But ...

... now more questions come to mind - Can CC really start accumilating if you are running high FC (8 - 10 PPM or more)? I would think not as anything under 1/10 of the chlorine you put in would be burned off (I am assuming that the pool started at 0 PPM CC and CYA is under 50). My pool was at 0 CC when I noticed I had no CYA.

How long do you need to keep a high chlorine environment? If you put in 10 PPM FC at 6 PM and you test at 6AM and have 6 PPM left, hasn't the chlorine done it's job. I always thought that as long as you have a FC residue that there isn't any more that the chlorine needs to do. (again CYA under 50). And wasn't the high chlorine in the tub burning off the CC as it was forming?

In my mind, a "shock" really isn't a specific quantity - it can be as low as 5 PPM FC or as high as 20 PPM FC, which is why I questioned the 15 FC figure for shock.

At this point with my pool not seeing a FC under 5 PPM since I started this post I would assume that any algea is dead. I actually put in 146 oz of bleach into my pool last night which yeilded 7 PPM chlorine added to what was there I was hovering around 11 to 13 PPM. I "shocked" the pool for the last time although I doubt there was a lot of CC in there.

[waterbear]

CC can accumulate, it depends on how much ammonia and urea or other organics are in the water. If you are killing algae then 0 ppm CC is a good indicator (along with the Fc holding overnight) that you have killed all the algae. If you do not raise the FC high enough to destroy all the orgainics in the water you will still have CC left.

Your example of putting in 10 ppm FC at 6 pm and losing 4 ppm overnight indicates that the chlorine is fighting something in the water and you need to continue to shock until the FC holds overnight when UV degredation of chlorine is taken out of the equation. This is a basic of the BBB method on here. Just read the posts!

"Shock" is really raising the FC high enough for the level of CYA in the water to insure that there is enough 'active' chlorine to do the job and it is not bound up with the stabilizer in the form of chlorinated isocyanurates but is in the form of hypochorous acid.

It is a combination of having no CC and having your FC levels hold that indicates that you do not have a chlorine demand in your pool. If this is not the case you need to continue shocking and possibly try shocking to a higher FC level. It is also important to keep the FC at shock level by adding more chlorine at least a few times a day.