Any idea what made the pH drop? Did you add anything else, and what was the pH before the drop?
At any rate, Borax is the thing to add now...I would start with about a cup, put it in through the skimmer slowly, give it a couple of hours to circulate, then retest and redose as needed. It'll be much better to "sneak up" on your target numbers of 7.2-7.6, than to try to dose all at once and overshoot it.
Just a note--high chlorine levels tend to give falsely high pH readings, so if your other pH levels were tested while you were at shock level, then you were getting false high pH numbers. If that's so, there's no telling just how low the pH is, since 6.8 is as low as it will measure, it could be a lot lower....so don't be surprised if it takes a lot of Borax additions to get it back into range.
With a CYA of 30, you need to keep your chlorine a little higher than 2. I would keep it at a minimum of 3, and prefer to keep it around 5. Also, you indicate that your total chlorine is 2, but your free chlorine is 0. Is that correct, or have you switched the numbers, considering that free + combined = total chlorine? If your FC is really 0 with a TC of 2, then you need to shock the pool again, holding it at 15 until the FC = TC, leaving your combined chlorine at 0. If you do need to shock the pool again, I would get the pH levels up FIRST, then shock it.......
Janet
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