My bad on the chart -- still got to add better indexing.

Yeah, algal and bacterial 'goo' has a HUGE chlorine demand, that must be satisfied before you can make everything 'all better'. However, given your high CYA, the bromine may be helping more than it's hurting, since the bromine creates a larger 'active' halogen residual than you'd have otherwise.

Given that you have a vinyl pool, draining is not a practical option.

But you likely don't have 35K gal; I'd actually flagged that. Here's the calculation:
18 x 40 x 3.5 x 7.48 gal/cft = 18.8K gal (top 3.5' slice of your pool)
18 x 18 x (8-3.5)/2 x 7.48 = 5.4K gal (assumptions: break at 20'; hopper volume is 1/2 of a non-angled bottom - reasonable for most liner pools)
Total gallons = 24.3K gallons.

Still, that's a fairly large volume, and the bromine may not be a long term problem. If it is, you can do a fairly effective drain, if you buy an over sized winter cover. I'll explain how, if that becomes necessary.