Cool, I don't use coco brick but I know it should be flushed with calmag.
Not to sure what the nursery might have but you'll definitely get or else Agri or online (I get all my needs from hydro store, just saves missioning around), sorry I can't help more there.
As for the watering. Let her dry out then give the next feed or water. Don't feed the next day again, wait till she dries out but not droop (you want your roots to have like a breathing action, wet - dry - wet -dry..)
Feel by the pot weight or stick your finger in there.
Looks like you might have a calmag deficiency.
I would suggest get hold of some calmag and give them a good flush.
I feed nutes then next feed calmag and so on.