What's on my glass?!

[clearwatersaquarium]

Hello all! I'm still learning (after 8 years) & all of a sudden see a few of these on the glass of my reef and in the bottom of my d/s bags. What are they? And are they bad or good?

 

[clearwatersaquarium]

Hello all! I'm still learning (after 8 years) & all of a sudden see a few of these on the glass of my reef and in the bottom of my d/s bags. What are they? And are they bad or good?

Oops pictures would help!

 

[Flippers4pups]

Need to post a picture to see.