Look at the new growth at the top, Its yellow/brown at the edges but not going very far twords the inside of the leaf. The further down the plant you go the worse the problem is.if it's nutes then just add some ph-balanced water to the reservoir. I'm not sure it's nutes though. Did they turn yellow before they went brown? My fan is a bit too strong and sometimes my leaves bruise one another and in time they look like your leaves.