You did predissolve the shock, didn't you? Also, you did drop the pH first like I said, correct? Most likely you precipitated out some carbonate (and lowered both your TA and CH in the process). This makes me suspect that your TA and CH were higher than you reported (and is a good reason to get a Taylor K-2006 and do you own testing rather than rely on the pool store!) THIS is also the reason I initially suggested using bleach, since it will not cloud a pool . It's not a big deal and it will filter out. Brushing will help. I would suggest getting your water tested (and ordering your own test kit).
Did you ever test the water from the cell to make sure it is working properly?

How are you testing the pH? Some pH tests will read high with FC above 3 ppm, another reason we like the Taylor kits. They are good to about 10 or 15 ppm. If you are SURE that the pH is 8.0 and not just an interference from the FC at 8 ppm or above (how was that measured?) then go ahead and add some acid to get the pH down to about 7.6.