What is growing in my fish tank?

It kind of looks like fungus by the way it's wrapped around something, though hard to tell. Doesn't look like it should be there though.

this white stuff is from the un-eaten/rotten fish food , i get this stuff when i give to my pleco his algae pellets and if i do not remove after few days this stuff grows back.

My suggestion do water changes 40% vacuum the gravel and try to feed your fish as much as they can eat in few minutes. if you have bottom fish then feed them before the lights goes out and take any left over fish food in the morning.

This white stuff can affect the water quality, as it is fungus which grows from left over fish food.

Algae....get it out