Chlorine lock - what to do?

Hi, I need some help understanding what to do with my pool water. We opened it about a week ago and I've done nothing but work on trying to get it balanced. It's now clear; for the moment. I do have a solid auto cover and don't know if I should have it open or closed. To make matters worse, it's HOT in Ohio (84 degrees today with SUN).

Background: about a 27K gallon pool. Water was kind of cloudy when we opened and did all the kits/chemicals we were supposed to do. I have what the pool store is calling a chlorine lock in place. My total chlorine is around 4 or 5 but zero free chlorine. My CYA levels are very low now. The CYA was super high at the end of last year but since the pool store been telling me all kinds of things and dumping shock into my pool at very high amounts with NO effect, I'm now lost. I just got done dumping about 1/3 of the water out and refilling it based on their advice. Yesterday we did a Phosphate test that read about 500 or a little higher so I added the correct amount of Phosphate remover. I've vacuumed it twice.

I've read on this forum that maybe I should shock it with Bleach (poolcalulator.com say I need about 3 jugs of 6%) for the CC of 5. What I don't know and need help is since the CYA is so low, will the bleach do anything???? I'm reading conflicting things. I also bought a bunch of Turbo Shock (Cal Hypo 78%) so I have that if I should use it.

Someone please help me understand what to do to get some Free Chlorine in this water. I'm not sure my pool store knows what to do. Thanks!