Pool Chemistry QUESTIONS

[PopcornGirl]

Rather than start several different threads, I thought I would combine all of my questions here, since they are all related to pool chemistry anyway.
I hope someone can help me figure all this out...

1) At what chlorine level does it become UNSAFE to swim?
I have just completed the task of shocking my pool with bleach (took a LONG while to get it to the 20 ppm and hold it there) and the chlorine level is now, slowly, on its way back down. (I think it's around 10 ppm right now)
I'm not trying to be an impatient child here, but I really am wondering: when will it be ok to swim?
5 ppm?
Or should I wait till 3 ppm?
Any idea how long it should take (theoretically) to come down to that?

2)I totally *get* the problem with the Taylor drops-based test kit -- the chlorine test bleaching out at the higher CL readings -- so I have been doing their recommended "High CL" alternative tests... But this got me to thinking:
If the high chlorine level can "bleach out" THAT test reading, then what is to prevent it from bleaching out the others?
The reason why I ask is this: I attempted to do a TA test the other night (with my CL near 20 ppm) and it turned weird colors! Instead of going from green to clear to red (as normal), it went from green to BLUE to YELLOW! It never did turn red. Even after 25 drops (and I KNEW that my TA was not that high because I just tested it last week). I repeated the test 3 times, each time with the same result.
At first, I thought my test chemicals had gone bad... but then I started to wonder about the CL level affecting THEIR color, too.
Now that my CL has come down considerably, I retested my TA and the test worked normally and is reporting my TA as being 120 (completely where I expected it to be).
Which brings me to my THIRD Question -- well, really, just an extension of Question 2:
3) HOW can I trust ANY of these tests while my CL is considerably higher than normal???
For instance, my CYA is now showing up as 35 when it was 60 & 55 just last week!
Is it really possible it has dropped that much so quickly???
Also, wouldn't this (the "bleached-out" theory) explain the unusually low pH readings?
I have added TONS of bleach to my pool in the past week (I have totally lost count on the number of gallons), yet my pH continued to *drop* all week.
Well, Is the pH REALLY dropping... OR is the color being bleached out by all the chlorine in my pool? Could my pH, in fact, be CONSIDERABLY HIGHER than the readings I am getting on the test?

Here are my stats:
In-ground, Gunite pool with exposed aggregate (blue/green) -- ~4.5 years old.
~12,000 gallons. CARTRIDGE FILTER
Water temp: 76 degrees
pH: 7.2
FC: ~10 ppm
TC: ~10 ppm
TA: 120
CYA: 35 ???
I have *just* cleaned my filters really well and I had to add fresh water to the pool this morning (AFTER these tests) because the level was getting a bit low (too dry lately!) I'm praying it won't stain again.
Sorry to be so long-winded (again).
Any help is greatly appreciated!

[larry2338]

Can just give you my experience and opinion regarding your question #1. I have swam a number of times with CL ~ 15 and CYA of ~50 with no ill effects and will undoubtedly do it again if the occasion arises.

[Mike_in_NJ]

re: safe to swim FC level. If you're not algae, it generally won't hurt you to swim in a pool with a high(er) FC level. It may dry your skin a bit more and may/will be tougher on swimsuits (especially the elastic parts), but it generally won't hurt you.

re: bleaching out of test results. Yup, that happens. What I usually do is to add a drop or two of chlorine-neutralizer (dilute sodium thio-sulfate?) to the test vial and swirl and then proceed to check TA and CH. I have rarely seen pH test bleach-out problems. Some test kits are more sensitive than others to reagent bleach out. Speaking of which, I need to get some more thio. <grin>

re: CYA and high chlorine. AFAIK, the CYA test will not really suffer from any bleach out problem with high FC levels. The test uses a different type of indicator than a color-change, it uses a precipitation reaction with the CYA (which makes the milky/cloudy mix that you then try to read when the black dot disappears).

As to where your CYA went, the algae most likely ate it. Really.

[waterbear]

Rather than start several different threads, I thought I would combine all of my questions here, since they are all related to pool chemistry anyway.
I hope someone can help me figure all this out...

1)

2)I totally *get* the problem with the Taylor drops-based test kit -- the chlorine test bleaching out at the higher CL readings -- so I have been doing their recommended "High CL" alternative tests... But this got me to thinking:
If the high chlorine level can "bleach out" THAT test reading, then what is to prevent it from bleaching out the others?
The reason why I ask is this: I attempted to do a TA test the other night (with my CL near 20 ppm) and it turned weird colors! Instead of going from green to clear to red (as normal), it went from green to BLUE to YELLOW! It never did turn red. Even after 25 drops (and I KNEW that my TA was not that high because I just tested it last week). I repeated the test 3 times, each time with the same result.
At first, I thought my test chemicals had gone bad... but then I started to wonder about the CL level affecting THEIR color, too.
Now that my CL has come down considerably, I retested my TA and the test worked normally and is reporting my TA as being 120 (completely where I expected it to be).
Which brings me to my THIRD Question -- well, really, just an extension of Question 2:
3) HOW can I trust ANY of these tests while my CL is considerably higher than normal???
For instance, my CYA is now showing up as 35 when it was 60 & 55 just last week!
Is it really possible it has dropped that much so quickly???
Also, wouldn't this (the "bleached-out" theory) explain the unusually low pH readings?
I have added TONS of bleach to my pool in the past week (I have totally lost count on the number of gallons), yet my pH continued to *drop* all week.
Well, Is the pH REALLY dropping... OR is the color being bleached out by all the chlorine in my pool? Could my pH, in fact, be CONSIDERABLY HIGHER than the readings I am getting on the test?

Here are my stats:
In-ground, Gunite pool with exposed aggregate (blue/green) -- ~4.5 years old.
~12,000 gallons. CARTRIDGE FILTER
Water temp: 76 degrees
pH: 7.2
FC: ~10 ppm
TC: ~10 ppm
TA: 120
CYA: 35 ???
I have *just* cleaned my filters really well and I had to add fresh water to the pool this morning (AFTER these tests) because the level was getting a bit low (too dry lately!) I'm praying it won't stain again.
Sorry to be so long-winded (again).
Any help is greatly appreciated!

I will start by saying sorry for my long-winded answer (again)!
To anwer your question about the TA and other tests from Taylor...yes high chlorine levels will bleach out one of the two indicators in the second TA reagent causing the color to go from blue to yellow instead of red to green. Taylor documents this online and also in the Pool and Spa Water Chemistry booklet that comes with many of their test kits. The solution to the problem they suggest is to add DOUBLE the amount of the first reagent (which is a chlorine neutralizer) and repeat the test. If the colors are still not correct they suggest repeating the test with even more of the chlorine neutalizer reagent until the colors hold.

The pH indicator can also give a false reading under high chlorine conditions and can turn purple when the pH is acutally below 6.8 leading you to believe that your pH is 8.2 or above. (simplified explanation---just be aware that the reading is suspect when chlorine levels are very high) This is not bleaching out but some of the phenol red actually converts to a different indicator, chlorphenol red. Unfortunately there is no easy fix for this (some people put some of the chlorine neutalizer from the TA test in first but this itself can cause a higher pH reading than actual). Just be aware that if your CL levels are thru the roof your pH readings might be suspect if they show that your pool pH is VERY high!

I would have to guess that your high pH reading was done when the CL level was extremely high and then when it dropped and you tested pH again you got a truer reading! Don't know if that is actually what happened but it would make sense.

As far as I know there are no interferences to the CYA test but this test is one of the easiest to do innaccurately! Develop a procedure and do it the same way each time. What I do (and what seems to work for me) is make sure the water is at indoor room temp (if the pool water is cold) and read the vial at waist level in the shade whenever I do mine. I also let the mixture sit for 2 minutes and shake it again before I take the measurement. The important thing is to do it the same way each time. If you do it in the shade one time and in direct sunlight the next you very well might get a difference in the readings.

You can have complete trust in your drop based kit. This is the best kind of testing we can do without spending hundreds or thousands of dollars on fancy equipment and the results are more than accurate for what we need to know! These are not just the Taylor kits that have problems. Most drop based kits use basically the same reagents. Taylor also makes kits that use FAS-DPD for chlorine testing that don't bleach out but the other tests are the same. You just have to learn all the little 'tricks' to use your kit properly. When your chlorine tests show high levels (or bleaches out) just be prepared to make the proper adjustments to your testing procedures.

[PopcornGirl]

Thanks all!

Yep; think I just proved my theory... My CL is now down to about 4 and when I retested my pH it had increased dramatically (7.8). So I think that is what was going on...
And thanks, Waterbear! I have adopted your method of testing my CYA and it works! It's actually EASIER to see the dot and when it "disappears". My CYA today read: 40'ish, so I guess I'm ok.
Thanks again,