if those leaves below are glossy in RL (hard to tell in photo) you probably have fed a bit too much.
If that's the case, regular ph-only irrigations would start to see a healthier green within a few days... if near end and want to flush, it's probably safe to continue doing that unless you see the canopy quickly get decimated.
Without any green, it can't power blooming. You can flush better when you are familiar with a plant - like a clone. It's difficult to guess especially with less experience when to start. No worries. It's mostly "bro-science" anyway. I'd do it with that plant if the leaves were glossy though.. not as a flush just to fix a toxicity.
8 weeks completed? you don't have long left... if you see a a strong fade overcoming canopy, give a dose of ferts and have no worries.
if the canopy ever dies in a complete way, you might as well harvest what you can soon before it rots on the stem.