Help with green sand bed

[Richie Lloyd]

Hey guys
Tank is 5 years old
Been suffering with green algae on the sand for months now
I syphoned all the top layer of sand out. It was nice and white and only a few ml deep. However within a week it was going green again (not every where, just patches)
I have loads of flow. I added more as you can see from the pics the flow is going over the sand as it has totally blown away in patches.
Someone mentioned today it could be green cyano?
Thought I would add some pics and get some opinions.
Thanks

 

[reeferfoxx]

Looks like algae. Do you have algae anywhere else?

 

[GainesvilleReef]

Looks like green cyano to me.

 

[Richie Lloyd]

Yes keep getting loads in my weir
Ill take some more photos tonight (im in UK)