Dar grey stuff

[scotty333]

Guys, I was levelling my sand and half inch down in one area revealed a dark grey should I call it gunk?
Any ideas what it is?

 

[John Doe]

Biofilm?

 

[taricha]

organics in sand far enough down that they stay anaerobic tend to create these dark grey patches.
The actual dark material might be high in metal sulfides like Iron sulfide. It'll go back light colored as it's exposed to oxygen.
There could be some amounts of hydrgen sulfide (harmful) in those buried areas, so I wouldn't stir up too much at once.

At least that's my best explanation for this stuff.

 

[scotty333]

Thanks guys, I’ll leave that area be then

 

[Salty_Northerner]

organics in sand far enough down that they stay anaerobic tend to create these dark grey patches.
The actual dark material might be high in metal sulfides like Iron sulfide. It'll go back light colored as it's exposed to oxygen.
There could be some amounts of hydrgen sulfide (harmful) in those buried areas, so I wouldn't stir up too much at once.

At least that's my best explanation for this stuff.

That would be the same stuff back in the day when I used to use a plenum I'm assuming correct? That was nasty when I broke the system down over 20 yrs ago and pulled the sand bed out.. Almost die from the stank lol