test the ph in your soil,could be a nutrient lock out.over watered,cut back watering.over fertilized,cut back on nutrient or flush soil.under fertilized,i fertilize every watering but very mild.insects, inspect leaves,virus,temperature,humidity,lighting,fungus.maybe the genitics in that plant.i have even heard that the leaf has served its purpose and making way for youth.root rot, root bound(transplant too bigger pot and fresh soil,(lime has calcium and magnesium)if you mist sprayed or got fertilezer on leaf could be a chemical reaction wit the lights.it cold be a numerous amount of things i suggest try 1 of these at a time. tri this mix; mild fertilizer,cap of peroxide,cap of epsom salt,and a pinch of baking soda ,seltzer water,watered and mist sprayed(plants progressed in 48hrs)before mix ; plant fan leaves at bottom turned yellow fisrt,then spread ,only effecting older fan leaves.some wer even white.they began to develop gark spots on yellow leaves the ends would turn brown and work its way up.afther mix;some of the leaves veins turned green and then the whole leaf began to turn green,the leaves that had to much damge eventually dried up.but before i woul tri this i would look at all the things could be wrong.and start with wat the easy could be wrong like heat strain,humidity,wind burn,pests,over watering,under watering,over/under fertilized ,check ph in soil........ allways use peroxide in waterings the roots love it.
