Please elaborate on # 1 and 2.
They are fairly vague and can be interpreted differently.
1. Swimming space--The adult size of the fish compared to the dimensions of the tank
2. Number of fish--Goes along with #1, the adult size of all of the fish compared to the size of the tank; how many top, mid, bottom dwellars there are
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#1 is basically whether the fish is going to fit inside the tank and be able to move around freely. Does it have to bend it's body to turn around in the tank? Does it have room to move around and not just sit there all day because there is no room? If it gets startled, is it going to be able to go into a mad dash without crashing into the glass and hurting itself?
#2 is whether the fish has room to move around and not be bumping into other fish all the time, and whether a fish can get away when it needs to. 8 guppies won't take up too much bioload in a 10 gallon tank, but with no place for the female to escape the males, the females are going to be harrassed to death.
The top, mid, bottom dwellar part is whether there are too many fish that stick to the same level. Like keeping cories in a 10 gallon. 8 is the magic number again, just like before, the tank can handle the bioload, but those cories are going to be awful crowded down on the bottom.