Help! Worms in my tank

[Tan Tran]

I have 3 different types of worm in my tank:1st is thin and long, 2nd is thicker and shorter, 3rd is very tiny and have something like 2 antennas on the head (I cannot take a picture of this kind because too small).

My tank is 20 days old and has one hillstream loach.

I did some research and know that worms is cause of over feeding and decay organics but my loach is not eat anything beside algae in the tank (I know this because he/she poop a lot and my plants are growing).

I will add some fancy goldfish to the tank so I worry if these kind of worms gonna be bad for them

Another question about water quality beside worms: I do water change once every 5 days and ammonia is 0.25ppm and nitrate 10-20ppm every time. I have two large sponges filters in 40gallon tank. Will this going to be enough filtration for my fancy gold fish (I’m thinking to get 3-4 of them)? 

I attached 2 pics of the worms and 1 pic of my tank

[doktor zhivago]

Living creatures come in with your plants. They're all harmless detritus worms and crustaceans and bugs and stuff. You aquarium is alive congrats. 

[Biotope Biologist]

Sounds like you have rhabdocoela, planaria, and some sort of detritus worms. They are harmless and make good fish fry food or cleanup crew. 
 

I have heard of planaria attacking and killing shrimplets but I’ve never seen it. But my snail population suffered some heavy casualties