How long have you had the skimmer?  When did it start this random overflowing?  When's the last time you gave the whole thing a good vinegar bath including the venturi?  Fwiw, I also think that considering the water depth is a reasonable step.  manufacturer recommendations don't always turn out to be the best.  Setting a tile or two under the skimmer might be an easy solution.
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					Originally Posted by  MarkoD
					 
				 
				I have a csc250 on my 100 gallon total volume system. 
			
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 Fwiw, skimmer sizing has more to do with display volume than total system volume (within reason).  This is because of the potential bioload, and generally the bioload is a direct reflection of the display tank size.  Do you have a very light bioload?