Chlorine Lock? Draining pool only option?

Have a in ground gunite pool 30,000 gallons, that we've owned for 15 years. Just opened the pool last week, it was pretty clear with just some leaf debris. Only thing we've done so far was add 4 gallons of liquid chlorine and have had the filter running with the chlorine tablets via a chlorinator with 1" tablets.

Went to the pool store to pick up regular maintenance chemicals & have water tested and was told we have chlorine lock and the only way to cure is to drain it halfway down & refill with fresh water & then bunch more chemicals. Looking online, there seems to be a big debate on whether chlorine lock is even a legitimate thing?

Here are the readings:

Free Chlorine: 9.51
Total Chlorine: 9.51
Combined Chlorine: 0
PH : 7.4
Total Alkalinity (Adjusted): 16
Total alkalinity (Input) : 81
Cyanuric Acid: 195
Phosphates: 0
Total dissolved solids: 500
Copper: 0
Iron: 0
Manganese: 0
Nitrates: 0
Saturation Index: .01

Any ideas? Advice? Looking on here, everyone sure seems to know their stuff...was hoping someone could help me out. Thank you!

Not sure if I posted this correctly? I can see it if I log into my profile, but don't see it listed on the main page?

I see your post.

There's no such thing as chlorine lock but your CYA is very high. I'd guess as a result of use of tablets. You can run a pool with high CYA, there has been some discussion on this subject here on the forum. Have you read through Ben's Best Guess Chart?

Another note: We don't put much stock in pool store chemistry test - there's alot of reasons but suffice it to say that they are often misleading. We recommend the Taylor K-2006 kit for reliable testing.

Without a DPD drop-count chlorine test, like the Taylor K2006, you will not be able to manage the appropriate chlorine levels for a CYA = 195 (or anything in that range).

Also, the 2006 has relatively accurate CYA testing -- still not VERY accurate, but test strips are TERRIBLE for measuring CYA, even when read electronically. If you actually have CYA = 195, you'll have to drain 75% just to get down to a CYA = 50 ppm.

Get some polyquat -- it will get the pool from turning green, and get a K2006. Test your CYA with it, and then decide what to do.