yeah you know it's a sign of salt buildup in your pot but not that much as it is only very early at tips,no need to do anything for now.just keep nutrients at this rate or lower some.in order to prevent it from spreading.new withered buds I think you mean those newer growth right? they don't seem to have a problem everything is okay.but that old leaves purpling issue to be honest I have no idea what is it and I can't see any purple fan leaves in pictures.maybe your led lighting get confused?anyway no problem at all.good luck