Yeah Flush...
Could be combination of one or the other, or both, of pushing them too much, or they are starting to need flowering profile of nutrients.
So protocol = flush and give them light flowering nutrients directly after flush. Then start slowly pushing flower nutrients but they're looking dark green apart from the tips. So likely they've enough nitrogen nutrients. Could be some tip burn from too high salts in the dirt, hence the dirt is actually leeching the nutrients back down out of the plant.. like osmosis but reverse!
Flush them, then light flowering feed as TaNg suggests in his feeding schedule.