Can't seem to get any chlorine to stay in my pool. Have 7 3-inch tabs in the chlorinator and added 3lbs of shock last night, but still reading zero when tested at Leslies and via my own home test. Leslies says it is the infamous "Chlorine Lock" and to just keep dumping in more Shock until Chlorine rises. Is this what I should do? I have this greenish dust that has been coating a good amount of my pool floor and walls of late - so maybe the chlorine is being used up attacking that? I even added conditioner 2 weeks back based on Leslies recommendation as they thought that might be why I was losing chlorine.
Here's my most recent readings: