I am trying to narrow down the source, although that seems pretty impossible.
* I cleaned my tank with bleach before I filled it, so I am sure there was no bacteria there.
* I cleaned all my rocks in bleach for at least a week before rinsing and putting them in.
* The log was bought from the LFS, and advertised as pre-cleaned/treated. Although, there is a little colony of actual algae that started growing on it pretty soon after I placed it in the water. So maybe it was the log.
* I bought a used XP3 and didn't clean it. It had the micro-colony spheres in there, so it's quite possible that is the cause...
*Sand was new.
*Plants where all bought from a reputable LFS.
*Could be in the local tap water? Eh, I hope not.
Any thoughts?