The fact is there IS something in your well water. The important question is WHAT? It can't be free of chemicals and minerals for 2 reasons. First, that would be a very exhaustive series of hundreds of tests. The local lab will only test for a few critical chems and minerals based on toxicity and your location. The second reason is there isn't really anything left. And that argues with the 30ppm TDS
I would check for a few things at home. Most importantly nitrates and phosphates. 2 very common well water ingredients. Also copper if you can due to its toxicity to corals.
Depending on where you live, anything they may mine for nearby may also be in well water.