brown rust like powder

[Rikko]

Cyano and diatoms can be pretty persistent, too. Some folks with established tanks go absolutely insane scourging the surrounding area if a little bit starts to appear on their sand bed. You can usually discourage it with water movement (in addition to good water quality, of course). I tend to feed more than I should and am running skimmerless and rarely have more than a tiny spot of cyano at a given time. I attribute the control solely to my surge and the good current that the entire tank gets once a minute.