Air Formaldehyde (HCHO) DIY test kit - Know What's in the Air that Surrounds You (Pack of 5)

I recently ordered two of these. The kits arrived with a date 03/19/2018 on the box. Is this the expiration date or the production date?

Some of the mixed liquid got on a porous counter. Should I be throwing away my porous counter now? Not sure what chemical is used for this test kit.

I want to sell my 2006 fema converted travel trailer. it's below freezing in the inside, will this test still work?

How sensitive is this product to other volatile organics besides formaldehyde? Could a positive reading been due to the presence of another compound?