It is importaint to find the centre of gravity on each individual blade first and make sure that it is in the same place on both blades, then if a blade needs weight added, add it on the C.G point. If the C.G is different you will have to add the weight to correct this problem first, and then add balance weight to the C.G.

The main thing is, the blades weigh the same, and the C.G is at the same point on the set of blades.