I currently have 2 tanks up and running at the office. I don't have as much time as I used to so they are neglected
33gal with Clown Loaches, Rummy Nose Tetras, Lemon Tetras, Leopard Danios, and a few Oto Cats.
65gal with mainly African Malawi Cichilds.
At 1 time I had 5 tanks all going.
Fish rock but they do require a fair bit of maintenance. Overfeeding is the worst thing you can do. A hungry fish is a healthy fish! The other big mistake most people make is loading up a tank too quickly. It takes a long time for an aquarium to be ready for a lot of fish and they must be added slowly to allow the tank to build up bacteria needed to break down waste.
I used to have a 30 gal years ago and found it quite relaxing to sit and watch the fish. I gave it up because it was such a pain every time I got transferred to start all over again. Now that I have been in one place for years, we have cats, so I haven't tried again. I do miss it though and stop and admire tanks I see when out and about.
We've got a very basic 10gal tank in our toy room. Danios and Rosy Barbs that have been around for well over a year now. We went through two plecostomuses (plecostomi?) before we realized you actually had to have algae in the tank that they could feed on. Now the third pecostomus is feasting!
I must have really happy fish because there are days that they don't get fed. Wait a sec... be right back.
My son has a goldfish in a little tank with filter. It has no fins left and was as good as dead for awhile, floating upside down etc. Then just about the whole fish turned black but he seems much happier that way. Actually moves now and then. Been that way for a few months.