Timothy: The key to success with a Mandarin fish is not the size of the tank, but what the mandarin is eating. Mine is fed frozen mysis twice a day, and she eats with it relish. When I just purchased her, she was on frozen brine (enriched with spirulina), but wasn't exactly "pigging out". I switched her to mysis after I got the seahorse. I eventually realised that the the little guy will only take mysis that's been freshly defrosted, i.e. if it's been through the defrost/freeze process more than once, then she just spit i back out. Having a seahorse (captive bred, also on frozen) and a Tubastraea really helps, because my mysis turn-over is now very high, so everyone gets fresh food everyday.