Saltzgadum
Saltzgadum was a substance that wasn't normally picked up by the sensors of a  starship. It was an agricultural sterilization agent that was used in the kelp farms on Beta Tottoro IV, until the cost became prohibitive and it was subsequently discontinued.

Furthermore, along with invidium, lucovexitrin, selgninaem, and jakmanite, it was one of only five undetectable substances that could exist in a nitrogen-oxygen atmosphere and that could alter the molecular structure of glass.

Saltzgadum had not been used aboard Federation starships for decades, so it was ruled out as having caused the malfunctions aboard the  in 2366. ()

ja:サルツガダム
Chemical compounds