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					Originally Posted by WarDog   | 
	
 Thanks!  according to this,  the drum is approximately 50g, so does that mean that the tank itself is not really 90g? 
This has always baffled me. 
like i said, my 180 nearly got drained to halfway for a water change, and my 90 was within 5" of the bottom of the tank (Yes, i realize there is some rock in there)  but not that much!  I also had to pull 1/3 of the water out of the 65 gallon that is plumbed into this system... I feel like i am pumping out 100 "aquarium gallons" and adding only 50 "Barrel gallons" 
There has to be some explanation, since this 50 gallon barrel is standard size, i am assuming our aquariums are actually not holding as many gallons as they state. 
interesting....
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90 gal SPS display+65 gallon mixed reef
GEAR: Korallin calcium reactor, bio pellets, digital aquatics controller, Tunze ATO, MP40, 4 x Tunze 6105 w/controller, Reef Octopus Xp3000 ext, 2x250w MH, Futura LED.