Have you read H3ad's formula for coco?
Based on the Lucas formula.
He recommends 1 gram Epsom per gallon.
Don't see any deficiencies in your photos the plants look good.
I use 1.5 ml Calimagic and one gram Epsom Salts and my base, using RO also.
I switched from Canna nutes to GH Flori series a...