Last year I bought two short and flat-backed rain-barrels from a garage sale for $15.00, I've been waiting to use them somewhere ever since. So, the other day, I was looking at the side of my shed beside my planters - and thought "will one of them fit there?". I had already created a level base from old bricks, almost like a patio. The bricks were high enough off the ground for a hose to be attached to the bottom of the rain-barrel, so that issue was solved. Because the rain barrel has a flat back, it fir perfectly against the shed wall and does not impede my path to the side of the shed or chicken door, it's the best location. Another bonus and one to be seriously considered is the amount of sun hitting the barrel, thankfully it's in some light shade, sheltered all day. Goldfish are best suited to cooler more comfortable temperatures, I wouldn't want the "pond" exposed to the hot sun, cooking the fish all day.
To set up the rain-barrel pond you need to make sure it's on a level surface and in a stable position. Make sure you use a barrel that is designed and suited for holding water, bins and rubbermaid material is not designed to withstand the pressure of holding water longterm and you could have a problem months down the road with cracking and integrity. My rain-barrels already came with a shut-off spigot and I plan on using water fairly often by simply dunking a watering can or using the hose several times a week. This acts as both a watering device - but also a method of doing water changes for the health of the fish. The top of the barrel is open and I'm not worried about mosquitos, any larvae will be eaten by the fish.
For the inside of the barrel, I made a small "Jenga" like tower of bricks (made sure it's strudy) and filled the base of the barrel with some small rinsed stones. On top of the bricks I placed a bigger piece of flagstone to act as both a shelf for pond plants and as a shelter for the fish. The fish like to go under the flagstone when they see a shadow, this will protect them from predators, and the hot sun if it ever reaches the barrel. Alternatively, the flagstone will act as a heat sink at night and add some warmth. I placed a potted mini lily-pad on the shelf and bought two floating hyacinth, not only are they interesting to look at, they also protect the fish and help clean the water from the toxins created by the fish waste. Using and re-filling the water will also help maintain the water quality.
Supplies you'll need:
wide-mouthed rain barrel
spigot with shut-off
bricks
small stones
1 piece of flagstone
pond plants
small/short hose
1 doz feeder goldfish
goldfish food