Worms in aquarium water

[Pachonfx]

Hello all,

I have a 5 gallon tank that I used for quarantine fish running for like a week or so while I was on vacation(just with 1 decoration and a sponge filter). Before I left I had a fish that died for unknown reasons and I change 70% of the water after that. So I left the tank clean to my eyes.
To my surprise when I returned I have a tons of green debris that I don't even know what it is and also lots of red worms floating around.
So my question is, is this worm the one that perhaps kill my fish ? Is this something I can put new fish so they can eat them?
This is the first time it happens to me. I attached some picture for your reference.
Regards,

 

[StarGirl]

They are probably midge fly larvae. I dont know what the green debris could be.

 

[Pachonfx]

They are probably midge fly larvae. I dont know what the green debris could be.

Thanks for your reply StarGirl , that might be an option. Forgot to add that I left the tank outside so it makes sense.