Is that a bladder snail? If so I think I’ve had the same thing in my tank some time ago. My theory is that the snails leave these slime trails when they climb up or down. And since you changed the water tiny bubbles stuck to it and made it more visible.
Could be something else though, I’m not totally sure.
GalacticMayor 
hair algae?
should be dead bacteria, new tank? manual clean and water change, it will go away omce your tank cycled
Is that a bladder snail? If so I think I’ve had the same thing in my tank some time ago. My theory is that the snails leave these slime trails when they climb up or down. And since you changed the water tiny bubbles stuck to it and made it more visible.
Could be something else though, I’m not totally sure.
It’s thread algae, I have the same thing and it’s harmless