I have a 75 gallon tank with a hydor 450 canister filter. I have two heaters that a friend gave me. They are 300W and 200W. I was going to put one at each end of the aquarium. Is this to much and which one should I place at what end. For example would it be better to have the 200W or 300W near the outflow? Lastly, if this is too much for the size tank what wattage should each heater be if I want to use two? Thanks.