Even that part of the electric energy supplied to the motor, that was converted to mechanical (kinetic) energy of the moving water, will eventually be converted into heat as the wave gradually dies out. According to the energy conservation law, and because it cannot be converted into other forms of energy. Like, for example, if you shoot a bullet at a wall, all its kinetic energy will be converted onto heat when it stops (providing that the wall won't move). So yes, the heat generation will be same as 94w heater. Only, the heater converts the whole of supplied electric energy into heat, and the motor converts part of this energy directly to heat, and part of it into mechanical energy, which is then converted to heat. But yes, I would agree that 100W heater will have a small contribution to the temperature increase in a 800gal tank. It may be essential for smaller tanks, though.