Completely random citric acid question

[Tangdora]

Completely random question. Left a cleaning tank filled with citric acid out for a week after cleaning parts last week. Went to dump it tonight and it had this wicked surface film on top which was as thick as a thin wash cloth. Curious if anyone knows what causes this and what exactly this stuff is.

 

[EnterName]

Mold or some form of pellicle I suppose?

 

[PapaFishRocks]

Something I would NOT be touching with my bare hands!

 

[WildOne]

Thats a sporulating mold. The powder that was on top is spores, meant to get airborne, and the thin coat under is mycelia, often in combination with bacterial biofilms. There was a lot of organic matter in that container. You'll get the same by forgetting a cup of juice on the counter. No need to ask how I know.

 

[Decamicron Labs Verified Sponsor]

100% some sort of microbe that is eating the citric acid. Citric acid is readily metabolized by a lot of organisms (its an intermediate in the Krebs cycle in the metabolism of glucose). Some people use it to carbon dose.

The pH of citric acid does kill a lot of microoganisms, but not all. It is very useful as a cleaning agent because it is very good at chelating metals, so it can clean various gunk off of glass and other surfaces. For example, if you have rust stains on your glass or reagent stains inside of a Hanna cuvette, a citric acid bath will remove those.

 

[mcarroll]

I agree with the other guesses here, but I have a question about the picture.

What am looking at besides a sink and some fingertips?

It looks like the dark circular part in the middle (our guest organism) was superimposed over another photo of the fingertips holding something clear that I can't tell what it is.