Stocking 55 gal
 

how do you know haw many fish to put in a tank is there like a ratio or something to go by?

1 inch rule
 

usually the rule of thumb is only put 1 inch of fish per gallon, smaller if its a saltwater tank. That means if your tank is a 10 gallon, you should only put 10 neon tetras in, as they only get about 1 inch each. Make sure you use their maximum length instead of the length they are now for your calculation. also, adding more than that my put your tank at risk of overcrowding

ok thanks

If it is saltwater, DO NOT go by that rule. Don't even go by that rule for FW. Can you put a 12" Oscar in a 12gallon tank? I thought not. Some fish have huge bioloads and small bodies, while others are the exact oppostites.

that is the most unscientific theory i have ever heard. i would say any where from 4-6 medium(anthias) fish 3 large(angels) or like 10 small(damsels/chromis).