In defense of cedar

     I had a gnarly cedar stump in my aquarium (Juniperus asheyi--Ashe 
     juniper, from Austin TX) for three years with absolutely no ill 
     effects.  I found the stump partially buried and looked like it had 
     been dead for years. I soaked it outside in plain water (no bleach) 
     for 6 weeks until it sank, then I placed it in my 90 gal tank.  Of 
     course, it stained the water for 4-6 months, but that looked pretty 
     cool.  (Perhaps if cedar is still "green" it would cause problems).
     My Ancistris lived under the stump for three years, where he went from 
     a "cute" 3 inches to a gargoyle-like 7 inches.  Java moss grew very 
     well on the stump.  Other plants (especially Vals) grew well in the 
     tank.  The Ancistris and my false SAE grazed on the cedar the whole 
     time, keeping it algae-free.  They seemed to prefer the cedar over the 
     aquarium glass.
     There were no unexplained deaths in the tank during this time.  My 
     Ancistris, false SAE, angelfish, lemon tetras, and black tetras spent 
     three years with the stump and are still going strong.  The only 
     reason I got rid of the stump was to make room for more plants!
     Cedar does not rot, so it obviously has some means of 
     repelling/killing some bacteria and fungi.  Same goes for cypress.  I 
     submit that these two woods are more desirable in an aquarium than 
     wood that does rot (like the "driftwood" you can buy at an aquarium 
     shop that is actually a grapevine!)