Mandarins are beautiful fish and although I want one real bad in my 80 gallon reef aquarium I reluctantly pass on it! If I had a refugium then I would have one as they require alot of bugs to live or they slowly starve to death! Just my own opinion!
Beautiful fish indeed, but I don't have one because I know they do not do well i captivity. You are the very first person who I have ever heard that saw a mandarin eat flatworms. This concerns me because so many people who have flatworms will possibly go out and get a mandarin because they think it is a cure for flatworms....when generally they won't eat them and most starve. I may come across as sounding like a "B" but when people post pictures of beautiful fish that are hard to keep in captivity and people oooh and awww at them I just don't feel like a responsible reef keeper if I don't step in and give my opinion that these fish do not do well in captivity. Just my observation and opinion.
Generally I see the difficulty in keeping a Mandy is making sure they have plenty pods to eat. Other than that from what I've read and witnessed they, friend has a 5 yr old Mandy, they do just fine given proper husbandry techniques.
This is Ray, I have a mandy that eats flatworms and I have an internal refugium for the pods. However He has never decimated the population in my main tank and I feed him with supplemental rotifers, brine shrimp, zooplankton, etc. So far after 2 years he is going great. I do notice that he has figured out to hang out near the fuge outtakes though. That is where most of pods get swept into the main tank.