Bright red algae in one tank, and purple in another

[OdinValknir]

I have asked in various local facebook groups and forums for an answer as well as many, many, many Google searches and cannot seem to find an answer outside of cyanobacteria. But it doesn't have any of the characteristics of cyanobacteria such as smell and so forth.

 

One tank which is a more heavily planted 75 gallon. The algae on the glass and only on the glass is a bright red color and has to be scraped off. When I scrape it off it acts like green algae or any other algae on the glass and just clumps up and floats away.

 

Another tank which is a still somewhat heavily planted 40 gallon breeder tank. I have some black rocks with white minerals in them. I forget the name of the rock. And this algae only seems to grow on the largest of these rocks and it's like a deep purple color.

 

Any suggestions on what it is or help to get rid of it would be appreciated

[Expectorating_Aubergine]

Could be black beard algae. Sometimes it's reddish, sometimes it's brown. 

[Expectorating_Aubergine]

Could be black beard algae. Sometimes it's reddish, sometimes it's brown. 

[JoeQ]

It could be dead/dying algea in which case nerite snails or otos will clean it up. Here is an example from early on when I re entered the hobby

[OdinValknir]

This isn't a altogether new tank. It's been up since early December. I suppose the red stuff could be BBA that has died and I just didn't notice. But it hadn't grown on any plants or rocks in this tank. 

 

Anyone have suggestions on the purple algae on the rocks?