How many inches of fish to 120 liters of water?

Answer 1

The "inch per gallon" rule is a very crude method and should not be relied on heavily. A slightly better method is the "cubic inch per gallon" rule, which would let you fit about 30 cubicinches if fish (imagine each fish as a solid cylinder).

You will be able to comfortably stock about 30-40 small-bodied fish (small tetras), or 20-30 medium-bodied fish (zebra danios, medium tetras). Or, you could fit 3-6 larger fish, depending on the species. Use your best judgment and look for fish forums where you can get opinions on the specific stock list you put together to be sure none of the fish will be aggressive to each other and that the tank won't be too crowded. Make sure you look at the adult size of each species; it might not be overstocked while they are all juveniles, but when they grow up it may be.