I would use 3 or 4 Fluval E-series heaters. I think they are they best. They are microprocessor-controlled, have LED temperature readouts, and color indicators that tell you the status of the water temp. I think they are safer because the microprocessor is less likely to fail and over heat the tank, also with the color indicator, its easy to see whether is hotter, colder or the same temperature that the heater is set as. Also, using several smaller heaters prevents any one from doing much damage if it were to fail.