That's potassium deficiency for sure. I've seen it a million times - those crispy burnt edges on the older fan leaves, the rusty spots, tips curling up. Classic K def.

Makes sense with your timing too. Plants need way more potassium when they start flowering and you just came out of light stress which probably messed with uptake.

First thing check your pH. If you're in soil you want 6.3-6.8, coco or hydro keep it 5.8-6.2. Wrong pH will lock out potassium even if you're feeding plenty.

Switch to your bloom nutes if you haven't already. You need something with more K than N, like a 1-2-3 or 2-2-3 ratio. Don't go crazy with the PK boosters yet, just get back to a balanced feed.

If you're using a lot of cal-mag back off on it. Too much calcium and magnesium can block potassium uptake. Seen that happen a lot with guys running RO water.

Make sure you're getting good runoff every time you feed, like 10-20%. Helps flush out any salt buildup that might be causing lockout.

Pull off the worst leaves, they're not coming back anyway. Keep the lights dialed back a bit for the next week or two while the plant catches up.

What medium you running and what nutes? If you tell me your water source and what you're feeding I can help dial it in better.