Your ph is low ... FFOF is prebuffered at 6.3 + ... raise it to 6.5 to 6.7 to allow for drift.
Leaf is getting necrotic. Showing leaf issue with magnesium . Often happens with led grows and becomes a necessary evil.
Since your ph is too low , you are cutting into uptake range.
Even if it’s 7.0 it will work. But not “ softened “ water. You can add 1-2 teaspoons of calmag to next watering.
FFOF can run up to 6 weeks before sigas of depletion ( Strain specific ) , which in turn only needs a good top dress of FFOF ,
which is your main medium anyways. Top dress will not overpower plant since it has become conditioned to it.
FFOF top dress merely recharges host soil without guessing .... instead of mixing up a feed.
Cold temps interferes with uptake and also adds to misery , raise ambient temps so soil does not stay too cold.
Especially if pots are on floor.
