Also, 10 fc is only shock level if you have 10ppm or less cya... And from what I understand, if you have 10ppm cya you won't know it because the test is unreliable under 30ppm cya... But even if your cya is 10 or less, your fc really should be at 15ppm, the +shock+ level. That is the chlorine level you maintain when fighting something in the water... Correct me if I'm wrong here, poolforum mods.
Basically your chlorine is still too low and you might need to study the best guess chart in a little more detail.