you start with a slightly over-fertilization to come down with an under fert all mixed with a little overwatering. The environment look poor in light and air
you have some dark green leafs and other already damaged. seem to be an deficiency of nutrients but still could be an over-fert. try to check the outcome water from the pot to know exactly the substrate conditions
stop any fan (could damage more the leafs if not healty and rise the temp lowing down air circulation. In extreme cases you can give up the plant from the pot and start to dry with warm air the bottom
how much is the temp outside the tend where you pick up the fresh air? you need to have at least 10/15 degree less to be sure that you can cool down the temp in the tend