Physically removing aiptasia from rocks is a mistake. They multiply when disturbed. Below is an excerpt from the attached link.
"While for many this may be their first reaction, extreme care should be used in this method. In attempting to remove Aiptasia anemones physically, every cell must be removed. You can not simply cut them up or brush them off. All that will result is many more Aiptasia returning a few weeks later. Since Aiptasia reproduce (quite effectively) by pedal laceration, tearing or breaking them up only serves to help them multiply much more quickly."
Aiptasia Anemone - Information and Control Methods