dark patches in my DSB

[s1214215]

Hi Reeflanders...

I have dark grey patches slowly developing in sporadic areas of my DSBs. The sand is oolitic white sand - unsure of type, but suspect it's silica beach sand from here in Thailand - smelled salty when I got it, and didnt react to the acid test. Had an outbreak of diatoms when the DSBs were added when I moved recently, but its dying off now. All my live rock is old seasoned rock.

The patches are an odd roundish/ovular in shape. Are they benificial bacteria? they mostly occur deeper down in the DSBs too. As I said, my tank system (75 gallon main tank - 5 inch DSB) has just been moved and is at the end of it's cycling with ammonia gone and nitrite nearly gone.. My water flow is good, with a Rio 3000 with squid attached for alternating flow, a Rio 2000 with 2 duck bills splitting the current, plus the return flows from my Remora Pro and the 40 gallon refugium (7 inch DSB) which gets its flow from the ViaAqua cannister filter that pumps water through the chiller into the fuge. I seem to get a little detrius/diatoms on the surface of the sand, but not settling into any dead zones.. Will put some golden sleeper gobies in to address this once the cylings completed.

So what are these dark grey patches???

Brett
Bangkok

[scubadude]

Hi s1214215

Any chance you can get a pic of the dark patches? if the patches are not on the top of the sandbed then its probably nitrifying algae, if you see air bubbles forming in the SB then I wouldnt worry about it too much and definately wouldnt try and stir up your sand manually, if you can get some worms, nassarius snails, ceriths or semi-agressive sand stirrers they can work it at slow pace. If the dark patches are slimey and at the top then they very well could be cyano.