Split from shocking-and-fc-t38274.html Butterfly
Yet another case where the pool calculator and the chlorine/cya chart disagree. Yet now that I look closely it's a 6ppm discrepancy. Which is significant. At 40ppm CYA it's 2ppm off but at 60ppm CYA it's 6ppm off.
For some, the pool calculator values work fine for shocking. For others such as the OP here it doesn't. My question is (and this should probably be asked in a different thread...) how to know when to use the chart instead of the calculator's values? And, why is there such a huge difference in shock levels? If 1ppm below shock level can make or break a pool, 6ppm discrepancy seems like too much to say use one or the other, but the chart is more aggressive. It's a LOT more aggressive as CYA level goes up. Any plans for a happy medium between the two, or perhaps merging one with the other so there's less confusion?