That actually is something to worry about, but nothing major. You're not quite far enough into flowering to have your leaves falling off. The plant could probably use another 100 or 200 ppm's of nutrition, likely in the Nitrogen, Magnesium, Calcium, and Potassium departments. Extra Phosphorus right now might be called for... but within the same ratio as before.
It could also be that the plant is too tall and not enough light is reaching the base and these leaves are just doing themselves in.
Impossible for me to say either way.
Hypothetically speaking, if you've been using 5ml per gallon, up it to 6ml per gallon. If you've been using 10ml then up it to 12ml per gallon. About 20% more food is as far as you'd want to go. Run that for maybe the next two to three weeks keeping a close eye on the pH (5.8ish will help with the Mg uptake) and watch for any burning on the tips of the plants. If you see little brown tips immediately drop the nutrients back to where you have them now.
In Hempy buckets it's also important to keep a look out for salt build up because of the physical structure of the perlite and vermiculite. You will probably want to flush the medi periodically when feeding so strong to keep that from being an issue. Clear-X might be a good call to keep everything clean.