Pool "locked" per local pool store

So glad to find this forum. Our pool has had an algae problem recently. local pool store said it has a "chemical lock". Pool was fine until we went on vacation for 10 days and when we came back we had an algea problem(ran out of chlorine). Haven't been able to adequately resolve it. Although in the last few days it seems to have gotten a bit better. I've shocked it twice with 7 pounds of shock(. > each time. About 2 weeks apart. Most recent readings Showed Total Chlorine at 10+ppm and free chlorine at that same level. From what I've read about "lock", these should be different readings. I ordered a K-2006 kit today to do my own measurements. The pool store said the only way to resolve my problem was to drain the whole pool(34,000 gallons). The CYA was 120. The PH was 7.8.
I use Di-Chlor shock and 3" Jumbo Tabs(trichlor) for routine chlorination.
As of today my pool water is cloudy. Can't see the bottom of the pool. Any advice is much appreciated. Thank you