Keep in mind that your NORMAL chlorine level needs to be about 10% of your CYA level -- so 6 ppm in your case. You can go as low as 5% if EVERYTHING is perfect -- low bather load, no thunderstorm debris, good filtration, no trace of algae, etc -- but otherwise it needs to be closer to 10%.

'Recovery' chlorination needs to be 10 - 20% of your CYA level, (9 - 12 ppm), and is probably what you need at the moment.