Because there were so many questions about my pond set-up, I put this together with the hopes that it answers some of your questions.
Remember not to overcrowd your pond. Your fish need room to grow and
overcrowding makes for an unbalanced system and adds stress to your
fish. I'll eventually have to look into making another pond soon as my
fish get larger. Also be careful not to shock your fish when introducing them to their new home. Float the bag containing the fish in the pond water for 10-15 minutes, then open the bag and add a little of the pond water and reseal with air and continue to float for another 10-15 minutes before pouring them in.
Cost: purchased 3, for ¥500 at local farmer's market
Killifish, medaka メダカ
Cost: purchased 8, for ¥500 at local farmer's market
Beside being purdy water plants are important for 1.) keeping your water
clean 2.) sheltering your fish from critters and the sun 3.) providing a source of food.
Cost: free - collected & introduced from a nearby canal
I uprooted a couple of small healthy looking stalks and used a piece of wire to attach them to a rock.
Cost: ¥100 from home & garden center
I recommend just buying one of these; they're like zucchini in the sense that they're prolific.
I opted to collect rocks for two reasons: 1.) an established bacterial
colony which help to breakdown pollutants 2.) they're free. Also look for water snails that can help clean eat excess algae. You want to make sure your rocks are clean. Using any old gravel probably isn't a good idea. Clean, aquarium rocks are cheap and sold in all kinds of colors and sizes.
Tap water is treated with chlorine to make it safe to drink, but it can kill your fish. Treat tap water with a chemical decholorinator — found at any pet shop, or in my case the 100 yen shop — before introducing your fish, just follow the instructions on the bottle. I do a partial water change every couple of weeks, meaning I siphon out about 1/3 of the water and replace it with fresh treated water.
CONTAINER & OXYGEN
I feed my fish once a day a small amount of fish food. Be careful not to overfeed. One last thing, remember that this is a closed system so every couple of weeks you'll have to do a partial water change. This means, siphoning out 1/3 of the water and replacing it with clean treated water. Also the plants will take up water and water will evaporate so replenish it as the water level drops.
Whew! I hope I got everything. Honestly, this may sound more complicated that it actually is. Once you get everything going, it does a great job taking care of itself. Make it; you won't regret it.