Killer slime?

[Proteus]

Over the last few days I have had a brownish red thin slime growing in the corner. I used a turkey Baster to suck it up and changed flow in tank. This morning I came to find the slime returning and my dragon soul and blasto clinging to life. These pieces were in the area of the slime. I have siphoned it out with sand and cleaned area

What is this slime and how do I prevent it.
Water perameters are all 100%