Aquarium rock turned black

[TheMilkman]

I'm re scaping my aquarium and my rocks that were buried are completely black and black smudge when i wipe them off. Any explanations?

[knee]

Did the water have a sulfur smell when you removed the rock? 

[Schuyler]

What kind of substrate did you have? How long was it in there?

[TheMilkman]

On 3/1/2023 at 4:20 PM, knee said:

Did the water have a sulfur smell when you removed the rock? 

Not really

On 3/1/2023 at 4:35 PM, Schuyler said:

What kind of substrate did you have? How long was it in there?

Its a sand substrate and its been there for about 6 months

[mynameisnobody]

@TheMilkman that is anaerobic bacteria, it will grow usually deep in sand beds. One time, I had a 75 gallon with the universal rocks flat tan/ light brown background. After 6 months or so, I decided to remove the sand and replace it with something else. The portion of the background that had been buried was completely black. If the oxygen has been cut off, you’ll get pockets of anaerobic bacteria. You’ll hear @Cory speak about the different types of bacteria in our aquariums. Well, this is one of them. As for cleaning it up, you can scrub it, but if you have the patience, all you have to do is let it get a decent flow of water to anything stained black and it’ll take care of itself. Good luck and it should not harm anything.