Welcome to TFP, I'm glad you've found us! For what it's worth, I think you're seeing dead algae on the floor of the pool.
Couple of things to get out of the way: "chlorine lock" is a made up pool store term and doesn't
really mean anything. You have algae because you do not have a sufficient amount of chlorine for your level of CYA. This will inevitably happen when using chlorine tabs since most are stabilized. The water clears up temporarily when you "shock" because you're bringing your free chlorine level to a point where it can start to destroy a lot of the algae. Of course, as you've been seeing, it drops right back down again once it's depleted since there is still active algae growth, even if you can't see it. The TFP methodology, which you'll find is quite minimalist, only recommends two methods of chlorination: liquid chlorine or a salt water chlorine generator.
How are you currently testing? If you're relying on pool store testing,
stop. You will need to make the investment in a quality test kit: Either a Taylor K-2006
C or a TFTestKits.net TF-100/TF Pro. Both use the same reagents, but the TFTestKits models are a better deal for what you get. If you do not go with the TF Pro (which includes a magnetic stirring device), it is
strongly recommended that you purchase a Taylor SpeedStir to make testing signficantly easier and less error-prone.
To get started, I would read the TFP
Pool Care Basics. After that, check out the article on the
SLAM Process (Shock Level And Maintain), which you will need to follow once you have a good test kit. You'll need to know your
actual CYA number and pick up some liquid chlorine before moving forward with that. SLAMs are considered complete when you can pass an
Overnight Chlorine Loss Test.
We'll help you get this cleared up and enjoying your pool again.