DEFINATELY thrips larvae you're seeing on your leaves there.
Blue sticky traps attrack them.
SPINOSAD is most sincerely the way to go.
MONTERAY garden insect spray
Conserve NATURALYTE
Are 2 products I've used before.
A misting to your mediums surface is also advised as is the customary leaves top and bottom.
3 days apart with sprays.
SPINOSAD is OMRI listed.
Another much less organic approach is HOT SHOTS NO PEST STRIPS but be warned they are carcinogenic due to the active ingredient dichlorvos.
It breaks down quickly though in oxygen.
Its advised to turn off extraction during hot shots treatment to be most effective.
J