diatoms?

So my tank has been up and running for 3 days now. It is a 6 gallon fluval edge. In it is has about 6-8 lbs established live rock, 2 lbs dry rock, some sand pulled out of a fellow reefers tank (however sat in a bucket for a few weeks). I have 27 watts of LEDS running over the tank...5 10000k white and 4 royal blue.

Last night and this morning I have started noticing a brown/rust appearing something on my sand in the front of the tank. It is only on the sand and not the rocks. Wondering if I am starting to get a diatom bloom or is it some kind of detritus

 

Would it be time to start adding a CUC? I just tested my parameters and they are:

pH- 8.2
Ammonia- between 1-2
NO2- 0
NO3- 0-5 (closer to 0)
PO4- 2
Ca- 400-420
KH- 150-160
dKH- 8.68

 

I would wait til ammonia and nitrite are at 0. Then slowly add a cuc

 

+1, make sure that nh3, no2, and no3 are all 0 before adding anything.

 

sounds good, guess I shall wait while it cycles! Blah waiting