"Where to keep the Synchiropus splendidus?
If you are thinking about acquiring a mandarin the first thing that must be considered is the type of set-up or aquarium that they require for the best chance of a long and healthy life. Mandarins should only be kept in a well-established reef aquarium fully stocked with live rock and sand. Only an aquarium with plenty of live rock can support the biodiversity necessary to provide the continuous source of microfauna essential to this species well being. A well-matured reef aquarium that contains plenty of live rock and sand can harbor populations of amphipods, copepods, mysid shrimp and worms that are the staple of the mandarin's diet. Without a large sustainable population of live foods within the aquarium a mandarin will slowly starve to death.
In order to sustain a population of live foods within the aquarium a couple things are required. First, the aquarium must be large enough so that the mandarin will not quickly decimate the live food supply. I would consider a 50-gallon tank to be a minimum size to support one mandarin. Secondly the aquarium must be set-up for a long enough period that the micro-fauna population has become well established prior to the addition of a mandarin. An aquarium that has been set-up with live rock and sand for a year or more is probably a good choice. Thirdly, the competition for food must be kept a minimum. Mandarins don't compete well with faster moving fish for the available food. If the tank contains other species of fish, such as the six-line wrasse, that consumes the copepods and other live foods your mandarin may not get enough to eat.
Live Rocks and Sands
If you are still in the planning stages of putting together an aquarium that you intend to keep a mandarin in choose your live rock and sand from several sources. Using rock and sand from several different locations around the world should increase the biodiversity of life within your aquarium. It is best to use fairly large pieces of porous rock in shapes that are easy to stack together while leaving open spaces and gaps in between.
A deep sandbed with a variety of grain sizes will encourage the widest assortment of microfauna to grow in and on the sand. Amphipods seem to reproduce better in coarse sand and coral rubble while a variety of worms may flourish in finer sands. After the microfauna population has had enough time to become well established a mandarin can be introduced. The assortment of foods growing within the aquarium will be the main source of food to sustain these fish.
If you have a friend in the hobby with a healthy tank ask for sample of their sand. This can be a good way to import a starter of microfauna and microflora into your aquarium. On the down side, if your friend's tank has an undesirable parasite or worm you could import this also.
Refugiums
A refugium can be a great source of live foods for mandarins and other fish. Algae turf scrubbers, sumps and even separate aquariums can be used to grow many of the organisms that mandarins will happily consume. I have some extra live rock with a little sand in my sump to encourage the proliferation of these foods. You can purchase starter populations of several live foods to place in your refugium. If you live near the beach you can collect some types of copepods and amphipods yourself. You can collect copepods with a 90-to-130-micron mesh screen or sieve. Even specimens collected from cold water locations often reproduce in a separate container or refugium."
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