What do you use as a guideline for your stocking density? Is it a certain number per gallon? Is it a certain number of inches of fish per gallon? Is it based on the age and bio capacity of your tank? Or do you just wing it? It's an age old question and often asked by new members getting in to the hobby. The old Rule of Thumb is 1" of fish per gallon of water. However, the obvious answer isn't so obvious! The true answer is much more complicated and harder to understand. So what "rule" do you use, if any?