A bit more information: I'm thinking that my SSD does not support TRIM, so it asked and I approved the use of Zero Fill. I think it's this function that filled up my hard drive.
From Defraggler help info:
"The performance of an SSD is based around the time taken to write to a block. This is at its quickest when the block is blank (zero-filled). If there are no blank blocks left, blocks must be erased to provide space for the new data. This slows down the writing process. If there is no TRIM function available, the SSD cannot erase the blocks in advance.
To prevent this from occurring, Defraggler can overwrite all of the free space on the drive with zeroes so that there's a supply of fresh, 'empty' blocks available to be written to. This can take longer than a TRIM, and puts a little more wear and tear on the drive, but is a viable alternative for configurations that do not support TRIM."