Saltzgadum

Saltzgadum was a substance that wasn't normally picked up by the sensors of a starship. This 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 can exist in a nitrogen-oxygen atmosphere and that can 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 USS Enterprise (NCC-1701-D) in 2366. 

サルツガダム