Is this just a dirty sand bed or do I have problems here??

[BabyDee17]

I just got home from a weekend vacation, only to find that the top of my sand is brown, not completely, but its definetly there. I checked the params: sal 1.025, pH 8.2, ammon 0, nitrite 0, and nitrate 0. I only have coral and a cuc...but speaking of that, I cannot seem to find anything except my turbos..all the rest of the shells are empty and when I started I added a bunch of extras to my tank. Ive only had it about 3 months..im so confused.
20g w/ plexiglass top..room for gasses to escape i think. coral and my now "dead"?? cuc... can someone please help? Thanks in advance...

 

[BabyDee17]

it looks darker in real life.. and also, whatever it is, does anyone have a suggestion on what I should do?? thanks again

 

[54seaweed]

its cayno
cerith snails will eat it also maybe add more current I had same issue added a power head pointed down in center of tank
between the snails and extra power head it cleared up in about a week
as you can see in second pict