All the freshly laid turtle eggs I have ever seen have sunk to the bottom, not floated, due to the density of the yolk and amniotic fluid, so in all actuality, my first thought is that infertile eggs, possibly even yolkless eggs were laid. The only eggs that I have ever seen float are those that contain punctures which would cause a pressure change by allowing water and oxygen to enter the egg rendering it useless. Maybe the eggs were kicked around by the turtles feet as they swam, puncturing them. The jury is out. By the way, do you have male and female turtles, just female, or how recently were they aquired? Either way, you could always have the eggs incubate in moist vermiculite at about 84 degrees and see what happens. Two questions to ask yourself, as any animal owner should technically ask themselves once they choose to incubate eggs, breed animals, etc. do you have the space to accomodate all those new turtles, or homes to give them away to? As for your last question about making the pool more comfortable, I'm not sure where to start without knowing what it is like already.
-JG