u guys are thinking of goldfish... goldfish are not only the dirtiest fish there are but studies somewhere.. proved they are the dumbest too... I mean all these stories of fish pulling at thermometers.. banging heaters against the glass.. splashing around the top of the water to get attention.. U have to give the fish a little more credit than only 3 seconds.. have u guys ever seen a new fish in your tank not be afraid of a net.. then when u either have to take it out.. or accidentally catch it in the net.. ****.. from then on it runs and hides at the sight of a net..
Personally i believe fish can remember stuff for more than 3 seconds.. anyways.. off topic..
I have a 29 gal
w/25 lbs live rock in it..
30 lbs aragonite sugar fine sand
13 red legged hermit crabs..
5 astrea snails (i'll never get anymore cause they commit suicide too much.. hehe... but seriously i find them on their backs at least once every week or so..)
5 cerith snails (best snails i've seen)
2 "false" percula clowns
1 bicolor blenny
1 dwarf flame angel..
2 hawaiian feather dusters
and a CB shrimp..
Filter on it is a refugium i made of a 10 gal
tank.. (3 nassurius snails/3 cerith snails... grape caulpera.. 2" sand (w/2 lbs of live sand).. and 3lbs or so of tonga branch..)
also a tronic 100 watt heater .. oh and a cheap little coralife skimmer(need to get a way better one soon...)
I also hooked up a gravity fed auto top off system on the fuge. (under the tank)
The tank has been running for 7 months now.. (just added the dwarf flame a week ago.. and everything seems fine)...
I am soon going to be making this tank a mini reef.. but many of people have told me that i have overstocked my tank and i say.. well it looks good.. fish are healthy.. and all seem happy... and most importantly my water parameters are constant and safe.. w/a water change every 2 weeks
So I say overstocked is when your fish fight too much and are not happy with their surroundings.. there is no general rule of thumb when it comes to fish in the aquarium.. because ideally you'd only want to keep one fish per 60 gals.. but that is not cost effective nor pretty at all..
Just my 2 cents :P