Defragmenting an External Hard Drive on a Macbook Air
So I have a portable hard drive I use with my Macbook Air. It is a 4TB one that was gifted to my a year ago for Christmas. The problem is, the person who gifted it to me didn't realize it was a Windows based one that needed special software to be viewed on a Mac. I purchased the app and have been using it just fine. But lately space on the hard drive has randomly been disappearing. On my Mac that's never been an issue. It reminds me of issues I used to have way back when I used to have a PC. It makes me think I need to defrag it. But I have a Mac with a flash hard drive and use a mounting software to view the external hard drive. I can't find any de-fragmenting app that will work on my Mac. I know it doesn't work on the flash hard drive, but shouldn't it recognize the other kind of hard drive that is the external one? Is there any program I can use to defragment it or anything I can do to fix it. I don't have a hundred dollars lying around to buy another external hard drive right now to be able to copy the files to a new one.
MacBook Air 13″, macOS 10.13