Those COULD be still DIATOMS, give it some time and see if it passes,, Check you water parameters, I think your tank is in its final stages of the cycle process, how are your water readings? I would not add and goby to a "new" tank, I think they much better in more mature tanks,, dont overfeed, watch the amount of time you keep your lights on, and maybe think about some nassarius snail,, good sand stirrers... 1 or 2 every 5gallons..