How many fish could I stock in a 20gallon LONG tank, I was thinking of getting 3 or 4, I know the general rule is 10gallons to begin with then 5 gallons for ever other goldfish. The tank will be in my Dad's garage, so I was wondering during the winter season (where I live it can get to -23C or lower...) if I could just place 1 or 2 50watt heaters in the tank and would they be fine? Or would I be better off to take them inside during the winter months to prevent any possibility of freezing?