ive jus had a look in my tank and there is lots of stringy stuff floating off the rocks in my tank. it looks like cob webs is this serious only ive not long put my fish in and dont want to loose it can any one help please?

Do you have a picture of the "Cobweb" like substance as it will help out greatly in making an exact identification. They are kinda common from what I've seen and can be many things, but usually they are a mucous net sent by several species to capture tiny food particles which is harmless. It could also be a sponge of some kind.