coryc - Thanks a million. I am going to set it up right now. You rock. Mighty helpful for a "junior reefkeeper"
MiltonP - Mandarin dragonets are what got me into reefkeeping. No, I actually have no dragonets.
I plan to breed them.
Since you asked, I'll give you my $.02 worth:
They need tons of copepods, isopods, amphipods. They are
best kept in tanks with dozens and dozens of pounds of live rock to keep the pods flowing.
Despite being cute little psychedelic big-eyed frog looking fish, their nature is that they are absolutely voracious pred
ators. They will clean out most tanks of 'pods in no time.
Can they be kept in a 20 L ?
If, and only if, you get one (no more than one - no, really) that you see eating brine or mysis at the shop. Also, it really helps if you have pod piles (sections of PVC laying on the sand's surface where the pods can live without threat) and a refugium. The little predators will clean you out otherwise. ALSO - bakpak skimmers supposedly form great pod refugiums in addition to a more standard one. A sump helps too.
I have a friend with one in a 40 gallon. I don't like it, but he did it without asking me. He has a refugium and a bakpak and his Mandarin eats brine shrimp. He is lucky.
Can it be done? I believe so. But if you don't keep pods flowing and safe from your Mandarin, and have a dragonet that eats other things, you are basically killing it slowly. Hope this helps