The difference between B and H is a bit subtle. B is basically how strong the magnetic field is in vacuum, so when there's absolutely no matter around. H is like the strength of the magnetic field within a material. See the answer to the first question to see how they relate in terms of an equation. For the diamagnetic levitation equation I gave you, you would want to use B, since that's what the equation is asking for. If you're ever not sure, be careful to look at the units. T and A/m are completely different units, so you'll only be able to use B or H, never both. Unfortunately this is a very annoying and tricky part of studying magnetic fields. I think for the purposes of your experiment, you'll want to mostly be using B.