Deficiency or nute burn?

Exceso! Cuando el amarillo empieza abajo es deficiencia. Cuando el amarillamiento empieza arriba exeso!

Flushing won't help, this is a slight nitrogen deficiency due generally from changing to bloom nutrients too early, as cannabis still needs adequate nitrogen during the first couple of weeks of flowering, it is only mid to late flowering that nitrogen requirements really drop off. You could give them a half strength dose of grow nutrients to slow the further yellowing progression, but at this late stage, you can also just leave them be, they will continue pulling what they need from the old leaves to fuel flower growth, and this is why not defoliating is so important, - the ready made source of nutrition stored in the older leaves ready to be used for situations like this. Personally, I would give them a half strength feed of grow nutrients for their next feed, just to give them a bit of a boost, but omit the bloom nutrients from this next feed, before resuming with the bloom nutrients after this single "top-up" feed with the half strength grow nutrients. What I have been doing for 25+ years, is to continue with grow nutrients for the first stage of flowering, up until there are small tufts of pistils/budlets formed, then changing to half grow and half bloom for the next 2 - 3 weeks, then again changing to straight bloom nutrients through until harvest/pre-flush. This seems to produce the biggest blooms on plants that don't completely exhaust themselves before they are ready for harvest and end up a sickly yellow colour. I consider a bit of a "fade" as normal, but do not believe completely yellow plants can maintain peak cannabinoid quality to the end. For a guide on when to start flushing, please see the answer I gave BakedPanda (how long until harvest?) in the question on this page, right adjacent to your own question. Nice plants by the way! Hope this helps, Organoman.