Ballast tanks instead of buoyancy slider

Right now there's a buoyancy slider under advanced part settings. I think that being able to raise or lower buoyancy without any weight/cost/volume penalisation is unrealistic and could be improved (of course the buoyancy slider is cool for simplification, so instead of removing it I would move it to the tinker panel)

Imagine that instead of the buoyancy slider in advanded part settings we could have ballast chambers as an option along dead weight, changing the available volume in a fuselage and the price and having the option of filling them with water (with a slider over Fuel, so you would have Ballast volume and Ballast amount of water sliders).
Then you can give the player the option of venting all the ballast tanks at any moment or, if it is in contact with water, filling them, making the buoyancy control both more realistic/fair and more useful.