I think if you use canning (pickling) salt, it won't cloud.
Your lava is too heavy for the liquid in the lamp. (Or the liquid is too light for the lava. However you want to look at it.) One way to make the lava lighter is by heating it more. Try putting a 60w bulb in the lamp instead of a 40w and see if the lava rises to the top. If it does then get a dimmer to regulate it and keep it on the 60w. Make sure you use an A15 size 60w just like the 40w. That is the easiest and least risky solution. But if that doesn't work then you are going to have to either lighten the lava or add something to the liquid to make it heavier.