Nope, it's the creamy coloured stuff on page 2 of the thread wrapped around the bottom of the eheim filter with a cable tie strapped round it.
It's not a fine sponge, quite coarse, you can just see through to the other side in places but you'd have to be trying to get through, only a very small fry could weedle their way through it. I got it from Para Rubber, they said it was aquarium filter sponge and shaved it off a block, the piece I have is about 6mm thick - if you tell me the rough circumference of the inlet hose and how long it needs to be I can shove it in an envelope. Or you can come get it if you like, I'm still at same place. I can also take Sharkey back again if you like to keep my other one company but I think you are quite attached to those little guys :love: