Hi there. What have you tried?
I've had Berghia before and they are amazing, but they also die of starvation after the aiptasia are all gone. And you'd need a ton of them to beat hundreds of aiptasia.
Have you tried Aiptasia X? This is the best way to strike back hard in a single day if there are more than 10 aiptasia in your tank.
Shut all the pumps off. With the syringe, fill every aiptasia you can find up with a squirt of it. Then keep the pumps off for 30 mins. This will dramatically drop the numbers. Do this every few days.
It works.