According to the chart I have, 1.4 lbs. bicarbonate of soda per 10,000 gallons will raise total alkalinity 10 ppm. If I use BleachCalc on an 18 ft 3.5 ft deep pool, I get 6700 gallons so I figure that 0.94lbs of baking soda per 6700 gallons will raise the alkalinity 10 ppm. If this is correct then 12 lbs would raise her alkalinity by almost 130 ppm. Since the recommended total alkalinity from my chart is 80 to 150 ppm (and the maximum recommended level is 180 ppm) I would guess the odds are pretty good that she is now way too high. I don't know what the effects of that would be but there is a whole section in the forum on alkalinity so you might want to look there.

Peter