Well that crowding level is not necessarily good husbandry and the average aquarist does not have your skills at maintaining that type of tank. ...
It isn't really crowded at all with all the rocks and caves in there. At times the only fish you see are the percula.
The gobies hardly ever leave the immediate area of their burrow and the mandarins and the pipefish are all day long hunting for pods somewhere in the rock structure.
The clowns stay most of the time in or above their surrogate anemone (ceramic flowerpot) or explore the immediate vicinity - they never go into the cave spaces.
Only the fridmani are a bit more active with the male always trying to lure the female into his cave.
The trick is not quantity but selection of the right fish to go together - and of course their size. Only the fridmani and the pipefish have by now reached their maximum sizes. The percula and mandarins are still less half their maximum.
The fact that all (except the poor pipefish) are kept in pairs reduces inter species aggression to a bare minimum - everyone is just too busy with its own kind to go after others. Only the percula and the male fridmani sometimes quarrel over "airspace" violations.
I also do at a minimum 25% water change each week - often more, because I route all water for water changes in my QTs through this tank. This leads to up to daily 25 to 50% water changes at times.
And finally, this is just a holding tank until my new tank finally arrives (it's been delayed for a couple of months now - Grrr).
I'd also be interested in how long this tank has been up with all these fish, and what are the Mandarins eating.
The mandarins are eating pods and frozen brine shrimp. I have tigger pod cultures of in total larger volume than the tank. These cultures produce enough for at least one feeding of 1-2 ml pure pods a day. And I'm right now in the process of doubling that capacity.
The tank is also full with amphipods and Mysis but I doubt the mandarins are able to get many of those.
The trick is also to have a coarse gravel bed that provides enough refuge for small critters - a bare bottom or fine sand bed won't work.
This tank has been up for 6 months and these fish are for the most part in there for 4 to 5 months.