The 2 most likely culprits are either zoa eating nudi's (that is the only thing they eat, so they would not be responsible for your leather issue), or the Asterina starfish.
If you see 10 asterinas on your glass, then I guarantee you, there are 50 more on the underside of your rocks where you can't see them.
Until you develop an eye for seeing nudi's (they take on the color of the zoa they are eating and are extremely good at blending in), though you may get lucky and find them on your zoas..or on the tank glass if you surprise them and turn on the lights while it is dark. No, leaving your blue LED's on at night won't help with any other critters you suspect).
Oddly, zoa eating nudi's do not eat all types/colors of zoas..I have no idea why and unfortunately, they do seem to like the more expensive ones...
You can use just about any coral dip (I like diluted Lugol's Solution), and leave the frag in the solution for about 5 minutes, then swish it around in there to see what falls off. You must ALSO check for EGGS, as they will not fall off OR die from ANY dip. They look like little tiny white spots in a swirl pattern and are typically found on the side of a polyp. You would need to cut off that polyp (IMO no sense in trying to scrape them off, it you miss one, you're screwed, better to sacrifice a polyp..)
You would need to dip EVERY one of your zoas (you won't find them on other corals) and you need to do this once a week for about 3 weeks to make sure they are all gone.
IF your asterina stars have ANY color to them aside from being TOTALLY beige (front & back), then they are the type that eat zoas and you need to get rid of them. I would not bother with tearing your tank apart..better to get a Harlequin shrimp. The downside to a Harley is that once they eat all of the asterina's you HAVE to feed them star-fish or they will die (they eat nothing else). People who keep them typically feed them a chocolate chip star once every 3 or so weeks to keep them alive.
I would also suggest that unless you have a reason to have those emerald crabs in there..you should rehome them. They are likely not your issue, but why take the chance? I do doubt it is them since your zoas are clearly - and systematically getting mowed down and we know you definitely have asterinas in there.
To catch the emeralds..use the beer glass trick..take a clean full sized beer glass..tie a little piece of shrimp to a piece of rock rubble and place it in the bottom of the glass. Prop the glass against your rock-work - use something to stabilize it there - and leave it there over night. The crab will fall in trying to get the food and won't be able to climb back out. Please re-home them if you catch them..plenty of people here with bubble algae who could use them
As far as zoa eating pods..very not likely. I've only seen one documented case and the pods were enormous!. Most pods will climb all over your corals at night, but they are only eating algae..so unless they are beyond gigantic, forget that as far as your tank is concerned.
If you see 10 asterinas on your glass, then I guarantee you, there are 50 more on the underside of your rocks where you can't see them.
Until you develop an eye for seeing nudi's (they take on the color of the zoa they are eating and are extremely good at blending in), though you may get lucky and find them on your zoas..or on the tank glass if you surprise them and turn on the lights while it is dark. No, leaving your blue LED's on at night won't help with any other critters you suspect).
Oddly, zoa eating nudi's do not eat all types/colors of zoas..I have no idea why and unfortunately, they do seem to like the more expensive ones...
You can use just about any coral dip (I like diluted Lugol's Solution), and leave the frag in the solution for about 5 minutes, then swish it around in there to see what falls off. You must ALSO check for EGGS, as they will not fall off OR die from ANY dip. They look like little tiny white spots in a swirl pattern and are typically found on the side of a polyp. You would need to cut off that polyp (IMO no sense in trying to scrape them off, it you miss one, you're screwed, better to sacrifice a polyp..)
You would need to dip EVERY one of your zoas (you won't find them on other corals) and you need to do this once a week for about 3 weeks to make sure they are all gone.
IF your asterina stars have ANY color to them aside from being TOTALLY beige (front & back), then they are the type that eat zoas and you need to get rid of them. I would not bother with tearing your tank apart..better to get a Harlequin shrimp. The downside to a Harley is that once they eat all of the asterina's you HAVE to feed them star-fish or they will die (they eat nothing else). People who keep them typically feed them a chocolate chip star once every 3 or so weeks to keep them alive.
I would also suggest that unless you have a reason to have those emerald crabs in there..you should rehome them. They are likely not your issue, but why take the chance? I do doubt it is them since your zoas are clearly - and systematically getting mowed down and we know you definitely have asterinas in there.
To catch the emeralds..use the beer glass trick..take a clean full sized beer glass..tie a little piece of shrimp to a piece of rock rubble and place it in the bottom of the glass. Prop the glass against your rock-work - use something to stabilize it there - and leave it there over night. The crab will fall in trying to get the food and won't be able to climb back out. Please re-home them if you catch them..plenty of people here with bubble algae who could use them
As far as zoa eating pods..very not likely. I've only seen one documented case and the pods were enormous!. Most pods will climb all over your corals at night, but they are only eating algae..so unless they are beyond gigantic, forget that as far as your tank is concerned.
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