CG is done with empty tanks.That way if you have a little fuel left in the tank it'll just make you slightly nose heavy which'll make it easier to land, not harder. Hmmm if the elevators are trimmed down to keep it level in flight that might suggest a tail heavy plane or the wrong angle of incidence on the wings but unless it needs a LOT of down it's not going to be of concern. Make sure your CG's right according to the plane's instructions and if there's a range given (eg: 105-115mm from leading edge) set it at the more nose heavy end of the range. Having it tail heavy won't make it floaty at low speeds, it'll make it stall-ey. What makes it floaty is the big, flat bottomed wing and the cure to floating is reducing your airspeed to reduce your lift.