Can’t add a goby or dragonet??

[CaliberGSD]

So I need some help here. I have a 40gal reef. My current stock is

Coral Branded Shrimp
Clown Fish
Six Line
Purple Fire Goby
Tail Spot
Royal Gamma

All smaller guys

Used to have a Green Brittle Star

I have tried 3 times now over the months adding a Sand Sifter Goby after my first one disappeared after 6 months. I have also tried to add 2 Ruby Dragonets (one after the other has died... read below) . I acclimate them for at least three hours before going into the tank. While in the tank they look like they are doing great and no one is picking on them.

I wake up the next morning and they are either gone or dead being eaten.

So I figured after some research it HAD to be the green brittle star. Traded him in.

Added another Ruby Dragonet. 3 hours of acclimating added him to the tank was swimming around and exploring just fine.

Wake up this morning and find a snail and the CBS eating him!

I know they are cleaners but.... could it be the CBS killing these guys? 2 Ruby Dragonets, 2 Yellow Head Goby and a Dimond Goby.

 

[Claus84]

I would have thought you would catch the CBS in the act eating the fish, I doubt it would just kill them. Sixlines can be nasty though so that's a possible culprit, it will also easily outcompete a dragonet in a small tank

 

[Claus84]

Sorry just re read and saw that you did see the CBS eating them, might be your culprit but the six line will also likely be an issue in time

 

[SeaJay]

I have falsely accused other fish then later come to believe the wrasse is actually the culprit. Mines not a 6 line though, so I’m not sure about their temperament.

 

[CaliberGSD]

The six line is a little guy and I have never seen him go after anyone. If anything he seems more scared than aggressive. Could be different in the dark suppose. But at the gobies also?

 

[mort]

Sixlines are well known for killing dragonets. I've seen several savagely attacking mandarins but they have been fully grown sixline and it will be during the day. At night they are tucked up in their little cacoons.
In this case though I think it's your shrimp. It's not uncommon for coral banded shrimp to be pretty predatory and a small stationary dragonet at night would be awfully tempting. Many people never have an issue with them but I had an old customer who's was a merciless killer of shrimp and small fish and I've read about problematic coral banded shrimp many times.