Dry edges of the leaves

if you have fed so little, i'd wager k-def... if the soil is hot AF, i might lean p-tox. 2:1:2 is a gret ratio, ask dr. bruce bugbee or any college level textbook on the subject. So, fill in some more blanks and make a best guess... easier to add than take away, if unsure. Since the problem occured so slowly, i'd react in a similarly small scale way... so you have time here to get it right and be safe. it is likely a very small change needed... i'd stick to that change for next grow from start.