Blocking Light in Sump?

[eternitybc]

Our sump is growing a massive amount of algae (and not the good kind). Our skimmer and equipment need constant cleaning.

Would like to block the light from the refigium and the rest of the sump...ideally we would have used black glass for that piece, but too late now.

I originally though of getting a piece of black non translucent acrylic, 1/8 or 1/16 thick. Then I was wondering if there are any other options? Is there anything thinner? I would have to get the acrylic or glass in 3 pieces to fit it in. Has anyone else used anything successfully?