Well, I don’t have a trick but I’ve been asked a lot about it. What I would tell you is to add a ton a pods for a good 3 months or just until you see a good pod population. For a 20, I would say you should not get a juvenile or adult. A small one like mine should be the best starter. I got mine from petco for $50, I believe they are 100 on Biota. Mine is a biota. Just replenish your tank with pods even though the mandarin might be guaranteed to eat prepared or frozen. Keep a good eye on them too, mine has been in the overflow too many times haha. Not a good time for me, but she was just throwin a munch in there. Make sure you have a ton of pods, have a culture or refugium to grow pods too. Even if your mandarin eats frozen or prepared, it’s good to have a pod growing place in case but also as some cuc for your tank and snacks for your other fish. Make sure your other fish aren’t aggressive either. Try not to have too many shrimps since they might get agitated. Good luck if you get one!