Mandarins have a different digestive system and metabolism than most fish. They need to be eating pretty much all day long to thrive. They can’t eat a big meal once or even a few times a day and be good, they process and metabolize the food quickly and need to continue to feed. You also can’t sustain feeding them mysis or bloodworms or pellets 20-30 times a day which is why pods are such a must for any mandarin. For mandarins that will take prepared foods it’s just a supplement to their constant searching for pods.
I would recommend doing some research into setting up a pod and/or Phyto culture until you are able to get ahead of the population in your tank. It can be done but its usually easier if you establish a very large population before introducing the mandarin as they can find many of them as they are introduced before they have a chance to reproduce in the tank so it can take longer to get a good population up at this point.
Long story short you need a self-sustaining/reproducing pod population to have a healthy mandarins long term and need a plan to figure that out.
Good luck