Dark green algae clumps in sand

[3eight33]

Hey everyone, have a bit of a problem on my hands. I feel stupid posting about algae but I need some advice. This stuff is covering my sand bed but not growing anywhere else. I do get a little film algae but that's about it. All test are coming up good with undetectable phosphates and nitrates under 5 atm. Lighting schedule has been the same for almost a year. I do run gfo that I change about once a month, or whenever the water coming out of the reactor shows any amount of phosphates. Whichever comes first. I can't think of anything that might have changed to cause this. Tank details are as follow, 100 gallon dt with another 60 gallons downstairs between my sump and refugium. Dsb and macros in the refugium. (macros do not grow, only have them as food) led lighting hung 8 inches above the water and a oversized skimmer (bubble magnus curve 7). Any other information you would like playing feel free to ask.

 

[Xavibear]

Is that sand or crushed coral? If it is crushed coral you should consider replacing it with sand. Try vacuuming those spots during your water changes.

 

[3eight33]

It's sand. Just zoomed in a bit to much maybe. I've tried to vacuum it out. It just shows back up and within a week it's just as bad.

 

[Xavibear]

Fighting conch & nassarius snails could help by keeping the sand stirred.