How many bags of Eco-Complete?

I recently set up a 55 gallon with 2 20 pound bags of Eco, plus 20 pounds of established gravel (it was a tank upgrade). I think 3 20 pound bags would do the trick.
 
I agree with 3 bags. I just setup a 55 with a outside layer of eco, and inside of sand. I used 2 Bags of Eco and it gave me a good base, three would have finished it off if i had not used sand
 
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