That would be it. The sponge is covered by a nylon and polypropylene mesh that has sharp edges. I have been trying to find a source for it and have been unsuccessful. One word of caution, the doobie actually does scratch the acrylic but only very very very lightly. I had been using them for years and someome told me they scratch and i said..no they dont been using for years..
So i went out to the garage and went to town on a scrap piece of acrylic. I mean, really went to town and you could see the fogging. Filled with water though you cant see them.
Anywho. I should take a picture of the tank. Been going crazy with the wrasses in the last couple months.
Leapord wrasse
Labout's wrasse
Male pintail
Yellow chested twist wrasse
Scotts fairy wrasse
Yellow tailed tammaron
Carpenters flasher
Exquisite fairy wrasse
Pink margin wrass
And a china wrasse
I really need to stay away from the fish store. Lol