This is excellent information. I’ll be dipping the starfish tomorrow, I’ll make sure to keep everybody updated on this.I only know of one instance of stars being medicated, and that was at Point Defiance Zoo and Aquarium for Sea Star Wasting Disease. It was successful, but I don’t know what antibiotic(s) they used. (I discuss this in my quote below.)
OP, I’ll let the others handle the parameters - the only thing I have to add to that conversation is that I’ve heard some inverts are particularly negatively affected by high magnesium levels (though I don’t think your level would be high enough to cause serious issues). With that out of the way, if you think it may be bacterial, I have some tips that may help with bacterial infections in my quote below (low temp, low nutrients, high oxygenation), and you could try some experimental antibiotic treatments (like the iodine dip discussed in the quote below - I have no idea how long a dip like that would take of you try it, I’d recommend reading up on relatively similar treatments before attempting it) and let us know how they go, but there is, admittedly, a nonzero chance they’ll kill your star before whatever this is does. (Speaking bluntly here, however, from what I’ve heard, there’s likely a decent chance your star will die either way, so, personally, if others think some sort of experimental antibiotIc treatment might be worth an attempt, I’d give it a shot - I’m not an expert though.)