Gravel help

[leannaby]

Hi all.. Cleaning out my tank today and I noticed in some areas all under gravel is black.. The gravel I have is natural so curious why this is and what is it.. ?? Will it harm my fish at all ??

Thanks

 

[LudicrouSpeed]

I got my tank second-hand from a previous owner, and when I changed the gravel I also saw all kinds of black gunk. I think it's just decomposed organic matter ... fish poo, dead plants, dead fish, etc... I cleaned out as much as I could which makes me feel better about it, although since it's already decomposed it shouldn't contribute to ammonia.

 

[leannaby]

It looked awful.. Had to give it a real good clean

 

[mrvincent]

Remove it with gravel vaccum. That's gunk.