that doesnt look like any algae Ive ever witnessed...
Are you sure the tank was 100% clean when you put everything in? It looks like some sort of foreign material thats reacting with the silt from the sand (you sand looks fine-grained)
Could be a bacteria. I did have some sort of bloom that clouded the water white. I had to use a cheap uv light to get rid of it. And it appears to be slowly coming back. Last night I added the uv light back on. It's a cheap hangon.
do you run any carbon source?
Try getting chemipure elite. the appropriate size for you tank.
it *should* take care of it within 2 weeks or so if its just a contaminant