Hi and welcome!

Your pool store is giving you a bum steer. Is your pH stable? That's all TA does: buffers pH.

I suspect your TA is NOW through the roof, and will take far more than 40 drops to get it to turn. If your TA was very low it would turn quickly. I would NEVER add 50 # of bicarb and my pool is only slightly smaller. So now you have a potential problem to fix that was totally their fault. Question: Did THEY sell you the bicarbonate, too, telling you it was "different" than Arm&Hammer? And charge you 3x what the A&H costs? (It's the same stuff).

Meanwhile, your CYA is VERY high--too high IMHO, and they didn't bother mentioning THAT to you! Luckily your FC level is fine for that CYA for maintenance. (over 100ppm we recommend a maint level of 8-15 of FC.)

If you are using Tri-chlor tablets or Di-Chlor powder STOP NOW! They are only making your CYA situation worse. Switch to bleach/liquid chlorine. If your CH level (Calcium hardness or just hardness) is low, you can also use Calcium Hypochlorite powder. It only adds calcium.

You CAN maintain your pool with CYA there as I said but you'd do better to drain 1/2 to 2/3 of your water and refill, dropping your CYA by dilution to the 50-75 range.

That's what too many pool stores do: Create problems where there were none so they can sell you more stuff.