I didn't read al these posts but mandarin problems seem to be a common theme on many forums. I really don't know why there are so many problems with this fish as they are an easy fish to keep and spawn if you just allow them to eat like they were supposed to eat. I also see that so many people spend so much on tiger pods and that is an expensive meal. A healthy mandarin will eat an entire bottle of those in an hour. Brine shrimp eggs are so cheap and easy. I have been spawning mandarins for decades and they just require a little different feeding methods than many fish but I di feed my pipefish, and ruby reds the same way and they are all spawning.
If you just let the mandarins eat natural pods in your tank, and your tank is not old or large, they may live a few years, but they will never be healthy enough to spawn and a healthy mandarin is a spawning mandarin because they spawn constantly. Here is an article I wrote about feeding them.
http://www.saltwatersmarts.com/diy-target-feeder-mandarinfish-pipefish-2804/
And a video