Which deficiency is likely the cause?

To me it looks like a huge overall nutrient insufficiency, combined with a mould/fungal problem as seen by the brown blotches. Unplug your humidifier, your plants do not need extra humidity and 65% RH during flowering is way too high, no doubt due to the combined use of a humidifier and DWC, which in effect is another humidifier. These problems should have been addressed weeks ago, it has really gone too far and there is little chance of rescuing any leaves, which means less energy production, which can only then result in less than prime flower production. These symptoms were already showing up 4-5 weeks ago in your diary. Personally, I would say the nutrients you are/have been using are basically crap. If I were you, I would feed my plants with proper grow nutrients for the next two weeks, in the hope that this will just and only just save the plants by stepping up the bud leaf growth, which isn't ideal, but your fan leaves at this stage would be producing very little energy and certainly not enough to sustain prime flower growth. After looking at your diary, the grow product you are using is rated at 0.23% nitrogen, has zero phosphorous and only 3.4% potassium. For grow you should have something around 5-2-5 NPK and your choice of bloom nutrients at 0.23-1.31-3.4 NPK is also very low on strength, for bloom, something around 4-4-6 would be far more complete. Try and get some products closer to those figures and this should give you a better chance of ending up with a better yield. And ditch the humidifier! Hope this helps,........... Organoman.