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					Originally Posted by gridley   the thought that it may keep me from scratching the tank and possibly damaging the tank if I was clumsy and dropped a rock. | 
	
 Dropping a rock while in water inside a larger tank won't damage the tank. Last time I removed a 1/2" piece of cross brace, I had to whack is 5 times with my framing hammer to actually break it. It's pretty strong stuff 

 Conceptually, nothing wrong with that extra layer, and especially a good idea to trim away the excess.