gross

Hi all. I’m a newbie to the hobby. I have 2 Oranda and 5 mystery snails in a 40 gal fresh tank. The only problem is it’s starting to smell reaaaallly bad after 3-4 days of changing the water/cleaning the filter. Ive added breakdown bacteria etc and I’ve tried using the basic stuff like candles...

I found this critter today. I am not sure what it is. Good or bad? Should it be killed with fire? Seems like a small orange worm with small white tentacles, or hairs, on one end and pointy on the other end. I hope the pics help. Thank you for your help!