I myself and many others have seen instances where a single mandarin will starve and wither away in a 90+ gallon established tank over the course of about 6 months. I personally wouldn't keep one in a tank less than 125 gallons, and the tank would have to be over a year old, and the little guy would already be eating prepared food. In other words, if you are going to get one, plan the tank around this fish, and don't keep ANYTHING that might compete for the same food. It is so sad to hear from people that are really excited that they are keeping a Mandarin successfully, it is usually after about 2 months that the owner thinks that the mandarin is in the clear and finding enough food, but if you look closely you can see the pinched emaciated stomache, so so sad. Mandarins will act just fine hunting for food as they always do right up till the time they die. Sorry to be one of the many that will give you bad news about this fish, but that's just how it is.