Algae on glass

Ok, so I have this algae growing on my front glass. I have no problem scraping off algae occasionally with the credit card, and every day with the magfloat.

But this stuff is absolutely killer. It's tougher to scrape than coralline. It's fairly slow growing, and grows back on exactly the same spots it was on before. It's reddish brown, and very thin, and slimy. When I scrape it, there's some sort of clear stuff left on the glass; these are the spots it regrows on. Anyone have an idea what this stuff is? I'll take a picture of the clear residual, but the actual algae is scraped already.

 

Turf?

 

I dunno. It's stupidly thin for how hard it is to scrape, which I'm guessing is because of its sliminess/slipperyness.

 

Sounds like cyano, but cyano isn't hard to scrape off. Weird.....

 

Try a razor blade. It could be that the credit card just isn't getting all of it off the glass.

 

Here's some pics, at different angles to make it clear what I'm talking about:


This stuff is reddish before I scrape the algae off. It looks like diatoms in that it's thin and slimy, but it sticks like heck, and is reddish-brown rather than the nearly straight brown of diatoms.

 

You mean like the big spot above the sun coral?

 

Sorry about that. Here's one of those pics with it circled.

 

Looks like its from the Radiolaria colonies.

 

I've found a couple posts through google on this stuff, but nothing on how to get it off the glass. A razor?