aiptasia meh? looks more like palys. anyway, u can should just remove all. if its palys, just take scissors and cut it off at the base. carenot not to et it come in contact with ur skin/eyes. POISONOUS! sometimes can squirt water. careful ur eyes. if its aiptasia, cut no use. will grow back/ suggest u use either peppermint shrimps, or copperband butterflyfish to eat it. Best is to use biological control, to eat the aiptasia. No choice then use chemicals.