Reef tank sand bed turning brown

[niche101]

I have been noticing that over the past couple of weeks, my reef tank sand has been turning brown. The tank is about 1 year and 2 months old.
ALK: 8.1
CA: 450
MG: 1350
Here's a picture. Thanks in advance

 

[saltyhog]

Difficult to say for sure from the picture. One with less blue might help. Possibilities include cyano and dinoflagellates. I kind of favor the former.

Can you give us some more information...how old is your tank, recent parameters (especially NO3, PO4), filtration. Does the brown go away with lights out? Does it look "snotty" or have bubbles late in the lighting period?

 

[niche101]

Ok,

Tank is about 1 year and two months old. I have been struggling with keeping phosphates down for a while,
Phosphate: 0.6ppm
NO3: 20
Ammonia: 0
Nitrite: 0
I did a 3 day black out and it kind of helped but then it started to come back even after a water change.
There are no bubbles on the sand its just brown.

 

[Perthegallon]

Ok,

Tank is about 1 year and two months old. I have been struggling with keeping phosphates down for a while,
Phosphate: 0.6ppm
NO3: 20
Ammonia: 0
Nitrite: 0
I did a 3 day black out and it kind of helped but then it started to come back even after a water change.
There are no bubbles on the sand its just brown.

I’m a noob but that seems high for phosphates?