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!