Brown pellets on sand identification

[Mr. Wiggles]

Hi all. My tank has been doing well but I've been noticing these brown pellets on my sand. They appear to be adhered to the sand grains and have a swirl look to them under the microscope. Any ideas what it is or how I can keep my sand bed whiter?

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[nikon187]

diatoms and flatworms?

 

[Mr. Wiggles]

I think too big for diatoms, these are macroscopic, circular and seemingly hard and calcified. I can vac the and bed but then over a day or two this stuff popps back. I have some on the glass and frag plugs as well.

 

[Mr. Wiggles]

Any other ideas out there?

 

[AlSimmons]

Spirorbid worms perhaps? Why they're showing up in abundance on the sand bed is beyond me though. The rocks, glass, powerheads etc is more their style when it comes down to colonizing an area.

 

[CanhMan]

Following this thread...the microscopic pictures are cool.
I have the same issue which recently started after I refreshed and increased the amount of GFO. Is it possible to put in too much? Got some of this brown film on my fuge bed as well. Will try to adjust the flow and see if that helps.

 

[Mr. Wiggles]

Hmm...I've seen those worms elsewhere in the tank. I'll see if I can get some better pictures. These brown things almost look like a barnacle of some sort.