Better oxygen exchange

there are alot of factors and its very involved and takes years of research or alternatively you pay someone to do it for you... In aquaculture, densities of .5-.75lbs of fish per gallon are common and high end farms are approaching 1lb of fish per gallon of water with high turnover. Alot of common aquaculture figures are 1-5gallons of water per pound of fish. I could write you a story on here about all the variables.... staying with a common marine ornamental density parameter of .5"-1" of fish per gallon is a safer bet but you will still need to have high water quality to achive this.