Help needed - chemistry

[gemphx]

My plaster pool is 13 -14 years old. I am getting it replastered in a month or two, so don't want to empty and refill at this point, so need some help.
I attempted a slam over the past week, and now letting my chlorine come down. I am out of the R0871 so can't get exact reading at this point, but smaller test shows FC over 5. (I think target is 7-9 at this level)
CYA is about 80 (yikes).
My questions are these: With these high levels of CYA I know I need high FC. However, does FC that high make the PH test inaccurate? PH (after slam) currently showing 7.8 and I added acid to bring down to 7.2, but not sure that test was even correct?
How do I keep it swim safe and algae clear until I get it replastered? Do I need to do the FC drop test to keep it accurate? (ordering test refills)
Going on vacation and need to leave my daughter very explicit directions. Thanks for the help.

 

[YippeeSkippy]

Yes, a FC over 10 *does* make the pH test inaccurate.
How does your water look now? If you are performing a SLAM it is safe to swim during the SLAM as long as you can see the bottom and the FC is no higher than SLAM level.

 

[gemphx]

The water is clear and has always been clear, but I was noticing algae on the cleaner and hose and in the outlets. My husband had been doing the pool since he retired, and did not know about FC per the CYA levels, so he was just making sure some showed on the tester. He went on a vacation and I am now doing the pool. I slammed up to 28 for a few days. Used that because when I did my original cya tests, first showed about 65 and next 80. I hate that test !!
So, if PH test is unreliable with high FC , how do I test it?

 

[duraleigh]

So, if PH test is unreliable with high FC , how do I test it?

Well, you have to let FC go below 10 ppm. Why do you need to test it?

Do you have reason to believe it is out of the 7's? (I don't think it is)

 

[gemphx]

Are you asking why I need to test PH? Doesn't it need to be tested? and if I have to keep FC high, then I can't test reliably, so what do I do? It goes up regularly. Even when FC is below 5 and PH can be tested, it will go from 7.2 to 7.8 in a day or so. Is that normal? I think there is a leak in my filter causing air in the returns and I believe I heard that can cause PH to go up? But don't I need to be able to test reliably and really be able to adjust?
Also, with the chlorine. I know the test vials that have the chlorine on one side and ph on the other will not test high enough for my FC (I need to keep 7-9 with my CYA), but can I use it and just make sure that the color is more intense than the highest reading? Testing FC with the R0871 each time gets pricey. I am having to reorder chemicals and if necessary will order extra to do the FAS/DPD testing each time