Take a large vase, fill it with water, add a bunch of fish, and they'll live in it all year round. After a bit of experimenting, I learned how to make one. Here's how.
Go to Home Depot (or wherever you like) and buy a large vase. You can choose with or without glazing. You can also use just about anything. Cattle troughs are popular in Los Angeles and Palm Springs.
If you choose a ceramic vase, it'll be porous and you'll need to seal it. Go to the plumbing department and pick up a small can of swimming pool sealant. This looks like pale blue paint. Get a cheap brush as well.
You'll also need a way to plug the drain hole in the bottom of the vase. If you can find a rubber cork, use that. I used a bolt and nut, two washers, and two rubber washers. If the bottom of the vase is flat on the ground, you can use a few pieces of wood (such as stakes) or bricks to raise the vase.
Seal the inside of the vase with the sealant. Paint it with the sealant and let it dry for 24 hours. Paint it again for a second coat and let it dry another 24 hours.
Set the vase in place and fill it with water. Let the water sit for 24 hours so the chlorine evaporates, and then add the fish.
Add goldfish or mosquito fish. Pick out colorful fish with patterns. Goldfish will grow to five or six inches. These are ten for a dollar at any bait shop.
Feed the fish every few days. They'll eat pretty much anything. A bag of koi food (at any fish store) will last a year or more.
You don't need to clean or change the water. After a while, a biosystem will arise. Microorganisms will grow along the sides and bottom. They live on the waste from the fish. These bacteria are safe. If your vase doesn't have these bacteria, the fish will die. There are two ways to get these bacteria to grow:
You can add them. Go to any aquarium store and buy Biozyme. This is a small container with the bacteria in powder form. Throw in a large pinch every few days for a few weeks.
If you know someone who has an established freshwater aquarium, ask them for a handful of gravel or a used filter from the aquarium. Drop that into the vase to get the culture started. This is like making yoghurt by using a starter culture.
If the water becomes cloudy or smelly, don't change it. The worst thing you can do is to change it. The water is cloudy because there are no bacteria. Add Biozyme or gravel from an established aquarium. It'll clear up after a few weeks.
The fish can live outdoors all year. In winter, it gets to the low 30s here. The fish don't mind.