Blue-green 'algae' is usually caused by low nitrates, organic waste build-up and poor water circulation. Generally this is coupled with a high/too long light period.
I get it in one of my tanks that receives a direct hit of afternoon sun, and I usually just manually remove it.
However, I had it growing along the substrate in one of my tanks and I just started gravel siphoning more often, dosing nitrates, and removed the baffle from my filter to allow for more water circulation.
It essentially cleared up in a couple of days, and never came back.