I went to upload some photos and videos onto my macbook air and was told there was not enough free space, so removed some things onto an external hard drive and emptied my trash. I now have over 30 gb free but I still get the warning saying my hard drive is nearly full. How can I fix this?
I would recommend looking at using a utility like CleanMyMac 3 to go through and perform some system maintenance and free up extra disk space. The first time I ran it on my system I freed up about 20GB of hard drive space by getting rid of language packs that weren’t needed by my system. It will also go through and clean out duplicate and unneeded version of photos from your iPhoto library.
Also, make sure to reboot your system at least once a week. This will let the Mac OS do it’s own system cleanup that doesn’t happen until you reboot your computer.