Gravel

About 1lb per gallon is a good starting point....then you can adjust +/- depending on what depth you want it
 
How many lbs of gravel did it take to get an inch deep in your 30g ?

Double that amount if you want it 1" deep

65lb would probably get you around 2" deep in your 65g
 
you can use as little or as much as you want. keep in mind that the deeper the gravel, the more room for crap to get trapped down in it, and the longer it will take to clean every week. plus, the more gravel you have, the less water will be in the tank.
 
Not only the area of the tank - but also the density of the gravel's material. For example, if you use something like Soilmaster/Turface/Aquatic Soil as your substrate you will need far less weight, as these are extremely light products.
 
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