What is this white string growing? Id plz

[nanomania]

It was 1cm, in a week it became more than 1 inch.

 

[DeccerZ]

Hey. Looks to me like a spaghetti worm, I have them in my tank, and they build little tunnels from sand... do you see any tube like tunnels of sand on the surface of the substrate?

 

[nanomania]

Hey. Looks to me like a spaghetti worm, I have them in my tank, and they build little tunnels from sand... do you see any tube like tunnels of sand on the surface of the substrate?

Its not a worm as it doest react at all, its growing on a frag plug. Its not an algae too. Appears to be sponge like, never seen such a sponge though.