what exactly is tubifex?.......

Sludgeworms. Long thin red worms.

YOu can also get tubifex cubes, which are little cubes that stick to the tank glass and slowly dissintegrate. There's one in my tank right now.

do u recommend any? worms or tubes?

where can i get these worms?

I used to feed my goldies live tubifex worms.I buy them at a breeder's shop.I'm not sure if their that good but the goldies will surely love them

they'er very good for young goldies as they'er very high in protein