I do believe this to be calcium deficiency and possibly some other micro nutrients.
Fox farm trio is notorious for “cal-mag” deficiency as it doesn’t have any.
General Hydroponics Flora series is a “trio” that does have calcium and other micro nutrients.
As well as General hydroponics maxi series.
Im not suggesting you change it up now, just something to think about when its time to buy more nutrients in the future 
I use General Hydroponics exclusively, both the trio and maxi series and it’s the smoothest most easiest grows ever…
Here my current grow if ya want to check it out, theres others under my profile if ya search through my posts.