Yep, your SLAM level (aka shock level) is 20 ppm per the chlorine/cya chart. Keep it up at that level, don't let it drop as low as it did if you can help it.
It is safe to get in the water at or below you FC shock value (20 ppm for your 50 ppm cya).
It is safe to get in the water at or below you FC shock value (20 ppm for your 50 ppm cya).