I would give it straight water and harvest in a couple days. You can also give it 14 hours of darkness or more now, not much growing going on, just ripening.
Rapid ph drops usually signal you have root issues, typically root rot. Either your basic bacterial rot or the super dreaded Cyanobacterial brown slime.
At any rate, a thorough bleaching after your run is standard practice for hydro.
Now just don't fuck up the drying.
Cheers