Any Idea What This Brown Stuff Is??

its only on my gravel and a couple of the fake plants, and maybe some on the dragon stone. I'm assuming algae of some sorts but I'm not sure.

 

It's algae for sure, just get a couple of nerite snails and you should be fine (depends on your tank though).

 

It's algae for sure, just get a couple of nerite snails and you should be fine (depends on your tank though).

ill try and get some tomorrow, theyll be safe with 10 lemon tetras, 8 salt and pepper cories, and 2 GBRs?

also do they multiply or no?

 

They should be fine, they don't multiply in freshwater unlike other snails. Whats your tank size though?

 

They should be fine, they don't multiply in freshwater unlike other snails. Whats your tank size though?

29 gal!

 

It looks like diatoms (aka brown algae). Diatoms are very common in newly set up tanks. While unsightly, they are harmless and will go away on their own in time.