Isn't that poor Starfish gonna starve to death, meester?
If the urchin is dead all the spines would fall off. I would get your parameters stabilized before adding anything else. I personally think it is too soon to add corals, but that is my personal view. What size tank and how much rock do you have? You may need more to be able to handle the bio load.
Xenias are pretty hardy not sure if they would work as an "alarm" as it would take a good amount to upset them. I would add more rock, I would rather have too much than not enough. Also depends on the type of rock you have. I would also test for copper just to rule that out as well. I had a problem with that and it really messed things up.
I know they're hardy but I've also heard that they are also quite moody and will stop pulsing if things are out, even before kits pick it up.
At the moment I'm going to avoiding adding rock as the bioload is low and I'm already causing stress by bring the salinity back down (albeit slowly) but will look into it asap.
Also, my new refractometer is showing specific gravity at about 1.031, so the hydrometer was clearly off. Hopefully I can resolve the issue over the next few days.
I'm assuming that your using coralife salt mix as I notice the high calcium levels..also I really think the salinity is too high.i usually test my water hours after I mix the salt in and do whatever adjustments needed to match the paremeters in the tank such as calcium,alkalinilty,magnesium and salinity