Any idea what this is, it appeared in my tank a few days ago.

[sue654]

It is transparent and about 3.5cms in diameter.

 

[Colin_T]

fungus covered food

 

[CaptainBarnicles]

Why don't you just take it out and look at it?

 

[Slaphppy7]

Looks like a dirty plastic disc or suction cup

 

[Sgooosh]

free food
anyway, you should just throw it out, i cant imagine that being any good to your fish

 

[vanalisa]

Verdict?