My Thoughts on Mandarin success
Let me start by saying I'm sorry to hear the outcome of your first Mandarin attempt and offer my condolences.
I do agree with Chort's statement regarding preferring wild caught to captive bred fish.(probably because I'm cheap and don't see the sense in paying extra for captive bred) I have had quite a few mandarins and to my knowledge none were Captive Bred. Although the mature tank only recommendation is not accurate.(I've kept mandarin from 3 months into my saltwater adventure without a fatality) I sold them for various reasons. However, our current Red Mandarin "Pudge" is appropriately named and a pleasure to watch.
In your earlier post you stated you have a hang on back fuge. How is it set up? I have a self contained CPR AF2SM(outlet is plumbed to inlet),that I quarantine my Mandarin in, and another on my 29G Hex, both are set up with 1 1/2" of live sand, reef rubble pile with a protected inner area made up of egg crate(2"Wx3"Lx2"H) stuffed with a dollar store pot scrubber covered with rubble and a "tennis ball size" ball of Chaeto(stocked with a bottle of cultured pods) floating around that I swap out,whenever I remember, for the Chaeto in my 6.5G sump with ATS.
When I receive them I place the mandarin in the self contained quarantine fuge. When feeding Displays I feed "mandarin quarantine" a small eyedropper from an old selcon bottle filled with Nutramar Ova, Cyclopeeze and Arctipods. After a month or so most will eat prepared foods along with pods and then I release them into Hex display.
So stick with it and don't let the naysayers tell you it cant be done.(It's not as difficult/impossible as some would have you think)