I've been keeping goldfish for many years, and I agree with the above advice: 180 US gallon tank and two excellent filters. I'd advise cleaning one filter one month, then the other filter the other month.
I'm not usually one to go for (sorry) cheezy accessories, but I'd get a large air pump and a couple bubble wands for aeration, as well. These fish require a lot of oxygen for optimum health, especially in warmer climates. I don't know what brands of air pumps are good these days, so someone else will have to answer that.
Since you said you only have "mechanical" filtration right now, I'll assume you don't know about biological filtration? If not, you can read all over the web on "biological filtration" and how to "cycle" a tank with fish, so follow those directions. You'll need a test kit to follow ammonia, nitrIte, and nitrAte levels. I recommend the Aquarium Pharmaceuticals (APA) Master Freshwater Test Kit.
After the tank is cycled, I recommend to find out how often to change your water to use the nitrAte test kit. You'll want to do enough water changes to keep nitrates below 20ppm maximum. There should be NO ammonia or nitrIte. Change the appropriate amount of water at least once every two weeks.
To change the water, I recommend you buy a Python No-Spill Clean and Fill. It will not only let you change water without buckets, but it will also let you suck the fish poop out of the gravel, which with goldfish is very important to keep wastes down. Just add your water conditioner before re-filling the tank. Make sure the water temperature is the same.
Make sure there are large decorations such as driftwood, rocks, plants, etc, for the fancy goldfish to get out of the current and rest, since they are fairly poor swimmers and will tire easily.
I hope that all helps! :)
BTW, try not to feed high-protein foods like bloodworms, because it can cause constipation and bloat. They should only be fed foods approved for goldfish. Or fed high-protein foods along with high-fiber foods like the centers of cooked peas.
Last edited by mfskarphedin; 07-01-2010 at 05:37 PM..