need help. can't keep zoas

[CoralOfDuty]

I recently purchased a 75 gallon from someone on Craigslist and upgraded from a nano cube. The tank was already fully established and looked like it was cared for. Livestock
Blue hippo
Pb tang
Sea urchin
Purple psuedo
Pink spotted goby
Maroon clown

So here's the deal. Everytime i put zoas in the tank they go missing overnight within 1 or 2 days. If i keep the zoas on a frag rack 1/2 inch from the top of the tank nothing can get to them and they stay safe. They have been untouched since i put the rack there a month aago.i started with giving away the urchin. Then the hippo. Then traded the powder brown. I even bought a harlequin to ensure the few asterina stars werent the culprit. I do not see anything that resembles nudis and would think they could get to the rack.
There are 3 fish left of the originals and don't think there is any way it's them.
There are 100s of colonista snails. Many brittle stars. Fire shrimp. Idk what to do. I'm ready to hang it up. This is terrible. And no the zoas aren't melting. Please help

 

[5thChorseman]

Could you have some sundial snails? They look like this

http://www.melevsreef.com/node/398

and can sometime be mistaken for colonista snails.

 

[vincent]

Or a scavenger crab?

 

[Geraud]

Sometimes with zoas it is hit or miss. Make sure there are no sediments on them though, that is one thing they really dislike.

 

[edd]

ck for nudis

 

[cmantis]

My money is on the clown flipping them. If its a big female maroon they are very territorial. I had the same thing happen with a toadstool attached to a pretty decent sized rock. Kept finding it upside down half way across the tank. Now way its the clown right....ha till I caught that b**ch in action.

 

[CoralOfDuty]

Thanks All. I set up a crab trap last night but no luck so far. I really feel like there is a xanthid in there. I have a bait zoa in a mason jar.