Black patches on my substrate

[devesh.r]

Hi guys

I noticed black patches on my substrate and my skimmer was pull out black stuff like a gel substance which has a really bad smell. Seems as something died in the tank even the substrate has this smell.

Can any tell be what it is. I'm current removing the substrate. As my water is lookin cloudy now.

Thank you.

 

[devesh.r]

No fish or coral died in the tank for a very look time.

 

[Juan27]

Could you post a pic?
You must really over feed badly for it to get that bad.

 

[devesh.r]

Sorry man never took a pic. Just done removing the substrate from the tank. The water was almost black with a bad smell.