HELP losing my clowns and don't know why

So here is the deal I have a 55 gal tank 2 powerheads 2 filters. Water has been tested every time I went to get a new fish and every time has come out perfect. I M brand new to this hobby. no experience at all. So here is the problem I bought my first clownfish Saturday. Had 2. Both seemed fine until I woke up and found my big fish was dead. Went and got another. That died within 8 hours. Got another he lasted 2 days and just died. But I found him in a hole in my live rock and he was missing his back tail!! I still have one clown who is still alive and is one of the originals. All the replacements are dead. The ones that died swim close to the bottom of the tank on the right side each time. the one that is still alive swims everywhere. After finding my fish with the missing tail. I am starting to think a hitchhiker is attacking and killing my fish. The only thing in my tank are turbo snails and blue leg crabs. Which i am told will not kill my fish. They are bottom feeders It is not my living clown either there has never been any aggression. I have found tons of hitchhikers in my live rock. Some good and some bad like aptasia. I also found this anemone in a hole. I think it is a ball anemone and it is not a nice creature has attacked my syringe when killing aptasia and I have read they will kill fish.