Just as a post for comparison, here is what I have my goldfish in. The important thing to realize is that I just upgraded my tank in March, and I'm already looking for a larger one. I think I'm going to have to build my own acrylic 120 gallon. Currently I do water checks weekly, and water changes at 50% 1x or 2x weekly.
75g
Aquaclear 110 and Fluval 404
Random small current creator and bubble wand
No live plants
Fish:
1 shubunkin, 9 inch
1 celestial goldfish, 5 inch
2 orandas, 6 inch
1 calico moor, 5 inch
6 bronze cories (mama keeps popping out more babies, I started with 3)
2 peppered cories
2 large dojos 7", 1 small dojo 3"
3 rubber plecos, 1.5" to 3"
1 ancistrus 4"
1 royal 3"
1 common pleco 4"
3 golden barbs
5 zebra danios (number is slowly decreasing - one of the goldfish is doing away with them)
4 denison's barbs
4 apple snails
2 ramshorn snails
temp is that of the house, which is rather warm now. at 77 degrees or above, i drop in frozen water bottles till it gets back to 75. during the winter, temp drops to approx 68. there isn't a heater.
these fish are healthy and GROWING, as well as breeding. i routinely get cory eggs and ramshorn eggs. i moved all the goldfish, the golden barbs, the common pleco, the dojos, some of the zebra fish, and all the bronze cories from central ny to boston with a broken tank, and they all made it.
Just a quick snapshot of what i've got. Here are some really poor poor quality pics. Water looks like crap cause I had a bacteria bloom due to a temperature spike.