Waste, Diatoms or Algae?

[Baigent87]

It’s been 4-5 weeks now and it looks like my 1st tank is now fully cycled. I’ve also started noticing these brown spots appear over the past few weeks and I’m unsure whether this is waste, diatoms or algae?

I purposely left my light off whilst the tank cycled, although the picture I attached shows the side of the aquarium that sees the most sunlight.

Any idea guys?

 

[T-J]

Brown dust on top of the sand usually is diatoms.
If you're referring to the brown and bubbles that is INSIDE of your sand bed, if I remember correctly, that would be your anaerobic bacteria at work.