Observation

[Beverly]

Brad,

My three tanks are all sandbed- and skimmer-free. The day before I do water changes, I clean the glass, then turkey baste the rock. There are so many crevices in the rock that crud just flies up into the water column. Some of the crud just falls back into the rock, I'm sure. Some of it falls to the bottom of the tank where I siphon it out during the water change. And some of the crud is pulled into the filter media in the Quickfilter attachments to my powerheads. Cleaning the media in outgoing changewater is an eye-opener, as the water is filthy. It takes several batches of changewater to thoroughly clean the crud from the media.

Based on these experiences, I'd have to say both sandbed and rock harbour lots of crud.