You can return them to your local store if you can find them. But as stated above you probably won’t see them to catch them. They only come out at night. Sometimes I’m told that when the aptasia are gone they’ll move around the tank and possibly end up in your filter sock. Then you can return them but I wouldn’t count on seeing them again. When I put them in I had literally a hundred or more aptasia. I thought the berghia had all died then after a couple months the aptasia started disappearing. Then they were gone.