Limestone is dissolved by water, hence the caves, and that adds hardness to the water. My record hardness is 136 gpg. With 100 gpm recovery rate, some of that water probably hasn't been underground for very long, meaning surface water infiltration in the groundwater your well is drilled into. And I suspect that the water table in your yard is rather close to the surface. Coliform bacteria lives in and on the ground and in the intestines of humans and animals and finding it in your water it is not good.
You can't use a UV light with hard water. So you need a softener that can remove the hardness. You need another test for hardness and then iron, pH, TDS, nitrates, nitrites at least and sulfates, chlorides and sodium would be really good.
Post the results when you get the test done. In the mean time you can learn how to correctly size a softener by visiting the sizing page on my web site. I suggest a softener using the Clack WS-1 control valve.