Name that problem (quick n easy)

Plant grown in promix.
Nuted lightly with a 1-5-1 organic nute.
Growth has been healthy, slow, and steady.
I am most perplexed by the disintegrating leaves.

This in my opinion is a Calcium and Magnesium deficiency and possibly early N deficiency. Pro mix is devoid of nutrients and if you are only using a minimal amount of nutrients your plant is hungry and will look and act better when you get this sorted.

^^^What Jimmy said^^^

Change you nuts to 3-10-1