The forums are moderated. New postings do not appear until they have been approved by a moderator. I have deleted your duplicate posting.
The Finder is incorrect because it is not taking into account the space occupied by various invisible files.
TechTool Protection and the Storage tab of System Preferences are correct, and agree with one another. The details are in this thread:
Tech Tool Protection showing incorrect disk usage?
Te warning comes from the Volume Usage pane of the TechTool Protection system preferences pane. You can configure it there. It is not configured through the TechTool Pro application.
It is standard guideline for Unix-based operating systems to have a minimum of 15% free space on the active startup volume. You have so little free space on the volume that if virtual memory swapfiles are created, they will be created in a fragmented state (in more than one piece), because the available free space is too fragmented to allow the swapfiles to be created in a single piece (called an "extent") each. You should try to archive some files to another volume.