I am in the process of setting up a new tank, 38 gallon, measures 36 x 12 x 18.
Main interest is in Angel fish so the question is:
How many Angels will a tank this size support along with Guppies and catfish?
On this website he discusses the bio load of fish. Interesting about a 4" vs a 2" fish. Of course, this is in general terms, and doesn't take into account the effectiveness of your filter and amount and frequency of feeding. But, it's still an interesting read https://aquariumscience.org/index.php/13-stocking/