Originally Posted by danbstrong
can also be light brown and almost black up the waterflow on it see what happens diatoms are at the beginning of cycle when you add new stuff you start a new mini cycle but if you havn added anything then i doubt its diatoms diatoms usually brown spots circles
This is not completely correct. First, adding new "stuff" will not recycle a tank, unless you intend on doubling your capable bio load. The intention of cycling a tank is to create the BB needed in-order to not recycle when new stock is added. (Enouph bacteria to break ammonia into nitrite into nitrate)
Secondly, diatoms is an algae that focuses on and only on silicates in the water. Most sand has some sort of silicate in it, and will slowly be polished off by the diatom when starting out a tank or moving the sand-bed exposing new silica.
I believe the OP will see resolve with his issue over time. Weather diatom or cyano
, it will disappear with good water quality (when the food source is gone).