Hi Gilly. I have that gravel vac.
it doesnt "remove the gravel" as you have posted.
It works in the same way as a gravel cleaner that siphons water out of the tank, except this unit returns the water to the tank.
When you set the unit up, you pour about a cup full of water into the black bit that hangs on the tank. This allows a vacuum to form in the plastic tubing, which sucks water up from the tank. Eventually the plastic tubing fills up, and water starts cycling from the tank into the cleaner and out (water returns from the black bit into the tank via a "vacuum bag" that filters out bits from the water.)
Because water is being sucked up the tubing, the wide bit (the bit inside the tank in the picture) can be moved around in dirty gravel.. the water flowing will lift stones up and mine usually get halfway up the tube. But most importantly the dirt gets lifted from the gravel, and stays floating in the water so as the water gets filtered before being returned to the tank the bits get caught.
The "filter cartridge" bit is naff. It is simply a sock placed over a plastic frame. The "series of inclined planes" dont atract dirt. They basically make a frame up for the sock to hang on. The water passes through the sock and so dirt is trapped.
I have a Roma 200 and the "bracket" doesnt actually fit over the aquarium rim. It does however clip on just enough for me to be able to safely use it. It is by no means safely attached though.
