Strange black growth on rocks?

[Kanevskystas]

Hi everyone!


So take a look at this picture.. This rock has two black spots like that... Feels like a leather chunk when i touched it with a metal tool...it is verry "slippery"




anybody has an idea about what it is ?

Also my live tock is constantly bubbling.. Also my cheota bush.... Nitrate final decomposition to gas out of my tank? I hope
Heres a pic...
My rocks lately started to fill up with huge purple and red algee spots... And i have tiny creatures crawling in every corner even on the glass...


Tank info:
20gal
60w cree led lights
With rocks crabs snails and a shrimp
Temp oscillating between 75-79 usually on 78
Recently added more pre cycled live rock...

 

[saltcreep1025]

i think all those black spots are called shadows =P

 

[Kanevskystas]

Im confused...

Its a physical thing.. Not just a color...
In the picture you can see that it looks like a black bubble..

 

[Tmar]

well i am very new to saltwater but I see the black you mean and it isnt even a regular shape... odd. Looks to me like some kind of spongey oil slick clingin to the rock....

 

[Texasreef]

How long has that bubbling rock been in the tank? With porous rock you should turn it over a bit when you first add it to the tank to get all the air out. If it's fairly new that could just be trapped air from adding it. Just turn it over to let it escape.