Why is my ssd's available space randomly changing?

I have a 250GB Samsung EVO 850 which currently has about 25GB free space. Once booted I can open My Computer and while doing nothing, watch as the free space randomly fluctuates until there is no space left on the drive.

Drive is less than a year old and was installed brand new into a new build. Problem started maybe 3 months ago and I am unable to find out what the problem is. I would greatly appreciate any help you can provide.

I have run SpyBot, MalwareBytes, and MSSE without finding anything.

Current PC Specs:

• OS Windows 7 Ultimate
• CPU AMD FX 9370 water-cooled
• RAM 8 GB 1600 MHz (Was 16GB, see below)
• GPU MSI R9 380 4 GB
• MOBO Gigabyte 990FXA-UD3 (Revision 4.1)
• PSU Thermaltake 750 Watts

Additionally the system was ruing fine until I had one of the 2 8GB RAM modules die. It was not until after the RAM failed that the SSD started to act up.

My drive monitor and 3rd party software all report the SDD is 100% healthy.

I want to install a new HDD for more space but not until I can figure out what is going on with the SSD and whether it will affect any new drives.

What could be causing this?