What Else Should He put In The 40 Gallon Tank?

at the pet store they can tell you how big a fish is going to get. so every one inch of fish is one gallon of water, if a fish will grow to be 3 inches it will need 3 gallons of water, you can only go up to 40 inches in a 40 gallon tank, don't put too many fish in or your tank may have some problems with ammonia.