Which Sharks???
Perhaps thayayballa needs to specifiy what shark he is talking about.
Goldfish may prefer cooler water but they don't require it. I have 2 comets in my 410 gallon which were originally put in as the proverbial "canaries in the coal mine". It is now 8 months later and I haven't had the heart to take them out and put them in a smaller aquarium. They started out as 10 cent feeder goldfish and are now about 4 to 5 inches apiece. I keep the aquarium at about 78 degrees Fahrenheit. They are showing no signs of stress. The only plant they have damaged is a weak water lily. No rivalries with any of the other fish either. Eventually they will get too big, but for now they are a gaudy splash of gold that I have come to enjoy.
Beasts
I think kois need around 1000 gallons..atleast acording to liveaquaria they do. I was thinking about getting a tattoo of one.
those are coldwater fish, but they get to over 3 feet long. they dont stay as good looking (if you can say so) as they are as juvies... adults are pretty ugly.I have been under the impression "Hi fin banded sharks" prefer cooler temperatures also, although they are okay in tropical. Let me know if I am wrong, but they get pretty large, like a couple feet large... but grow pretty slow and are supposed to be peaceful, and considering the size fancy goldies need, I would imagine you are going to upgrade as necesary or move them to a pond?