Originally Posted by Zombie
That would mean 100+ pounds for a 29gal. 50lbs for a 10gal. 25lbs for a 5gal. That seems like a LOT of gravel.
Something's wrong with the math here. One pound of gravel for each gallon of water would be 10 pounds in a 10 gallon tank, not 50, and 29 pounds in a 29g, etc.
But another point should be considered, namely, will you have rooted plants [=plants with root systems that need to be in the substrate] in the tank? If yes, you will need enough gravel to hold the roots and allow them to grow; 2 inches is usually adequate, or a bit more. If no plants, the gravel could be very shallow as it becomes simply aesthetic (appearance). The gravel substrate collects waste better than bare glass and it can be easily vacuumed off during the weekly partial water change.