For my final outcome I ordered some Ferrofluid and 2, small, strong Neodymium magnets. It came with a petri dish and pipette. This is a quick post showing it working.
I put the petri dish on top of my glass desk and used the magnet from underneath the glass. The thickness of the glass meant the magnet didn’t get too close to the fluid and made the perfect spike form. If the magnet gets too close to the fluid it does not create the spikes as they have such a strong attraction. I will need to bear this in mind for when I put my final outcome together as there will need to be a small distance between the magnet and the liquid for the spikes to be able to form.
My next step is to get the stepper motor I ordered working, and then I will be able to link the input of the Ping sensor to create the speed change in the motor.