Mold, fungus, or parasites?

So, I'm pretty sure this is the culprit that wiped out my entire fish family. I think I over fed and/or didn't clean well enough, being a beginner, and created a parasitic environment. I just want to see what you guys think and what's the best course of action? It's basically all around the back and sides of my tank.

No idea what that is never seen anything like it.

What kind of substrate are you using it doesn't look familiar, also is the yellow brown stuff on the substrate (right bottom) a different type of sand or gravel or is it waste. If it is waste you have too much.

They look like planaria worms, you can use Panacur to eradicate but search the web, there are some good instructions on how to use it safely.

Panacur is a trade name the active ingredient is Fenbendazole.