Hmmmm ... I don't know my diatoms (when I had them) looked like just a dusting over the sand and yours looks rather built up if you ask me.
I would say to do a water change, if you believe your LFS
has not changed their filters you may want to ask them, only IF you use strictly their water. I know my LFS
wouldn't have a problem with me asking. Increase flow to that are if possible. What size tank and what are your water parameters? And what kind of clean up crew do you have and how many?