Quote Originally Posted by vinnygnj View Post

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!