Wierd black spots in sand now with bubbles

[always learning]

I'm not sure if this is normal, good, or bad; I was looking at my aquarium (still cycling) and I noticed these wierd black spots in the middle of the sand. I used just regular playsand, quikrete, without cleaning it or anything and I put crushed and a few whole shells in there from the beach (cleaned) and I have a skimmer running and an emperor with activated carbon. Its a 20 gal. with 45 lbs. of LR and just about 2" of sand but I think I'll add another inch or two. I have a 10,000k coralife bulb wich I just turn on for a few hours a day for viewing. The tank is through about one and a half cycling weeks. I also noticed a few bubbles in there just tonight, what does it all mean?

Thanx,
always learning.

[kreblak]

The black spots could just be spots of diatomaceous growth concentrated into small areas, making them look black. As far as the bubbles, my dsb had them for over two weeks after filling the tank, as the dsb settled and air escaped to the surface. Most of the time the sand would stick to the bubbles and create little sandy balloons that floated around in my tank until being sucked into the powerhead intake. After two weeks, I didn't see anymore bubbles.

[liquafaction]

I still get those little sandy bubbles, and they stick to my power heads and plumbing

[kreblak]

I haven't gotten any in a long time. I have a really high current in the tank, though, and any bubbles that do pop up are quickly disposed of, so I wouldn't see them anyway.