[DonRotolo]

OK, the lava is mineral oil, and the fluid is some mixture of isopropyl and water. The instructions do say that it takes some experimentation to get it right. As with any experiment, take notes of what you do and the effect it has.

Oil floats on water. It floats less (sinks, actually) on isopropyl, since it is not as dense as water.

If the oil sinks too much, don't add alcohol, add water. By the drop, if necessary, until it works. If the oil floats, add alcohol. I'd use the 91% only, myself, since the other 9% is water, and water can be added by itself. (in other words, why add 30% water with the alcohol?).

Think about it, the answer will be clear.