What's a safe level? I have been maintaining a shock level of 20 but if I let is alone in the sun, it comes down pretty quick in a day. I was gone all day once this week so I didn't test and add any bleach and it dropped down to about 10 over the course of the whole day.I'd probably let the FC drop a few points below shock level and let them swim.
I think I did it right the second time. I had sun at my back, early in the day. The first time I wasn't really sure of the lighting and where the sun was so that's why IWell the CYA test should be outside in bright indirect light with the sun to your back and the tube at waist level.
Not sure what the differences were in lighting you were in.
If you think it might be as low as 30ppm, then I would let the FC drift below 12ppm.
Look for anywhere algae could be hiding. Ladder toy's things like that. Something in there is still consuming FC.
Yes keep your SWG off for the OCLT. Make sure pump is running for it also. Brush also.