Slight tip burn along with N def looks like lockout from fert buildup in soil and/or overwatering.
Your exhaust should be brinigng fresh, not recirculated, air into the room- if I mis-read, cool; if not, rearrange the ducting to allow a constant supply of fresh, cool air.
How lo9ng have the plants been in those pots?
Do the pots have a built in drain cup? If yes, remove it and smell around for evidence of rot- those things make drainage TERRIBLE in any pot and cannabis hates poorly draining soil.