Hi, Dazed.
Goldfish are the only fish I've concentrated on, pet-wise. They can live 20+ years, but the fancier varieties have more stringent needs than the common comet goldfish. You said you had a "bubble" head variety. Do you know if it is a "crown" (like on a pearlscale), a "cap" or "wen" (like on an oranda)? Also, does it have a dorsal (back) fin, or is it a bare-back variety like a ranchu or lionhead? Or even a "bubble eye" (with sacs beneath the eye)? Each breed has some particular issues which need to be addressed.
Some fancies like a little heat in their tanks - as much as 78 degrees. Professional breeders debate back and forth about heating a tank, but many problems are resolved with a little heat and a tiny bit of salt added to the water. (Though I wouldn't recommend experimenting with either right now. Salt can help with high ammonia levels, but there are other steps you can take before going that route.)
As was mentioned, the ammonia levels are going to be higher in a tank that is newly established or which has been "stripped" for cleaning. Ammonia levels also rise slightly when new fish are added to the tank. The beneficial bacterial take a while to catch up. You'll need to do larger and more frequent water changes until the ammonia levels go down, vacuuming the gravel during each change. Additives to reduce ammonia are nice, but water changes are the key. Don't panic and change the water when it gets cloudy - you've got a bacterial bloom going and don't want to disrupt it. Since you'll be doing a lot of water changes, I'd recommend a Python system - they make changing water and vacuuming gravel a snap. Ask about it at the pet store and they'll help you find one suited to your tank size.
There are supplements you MUST add to tap water to remove chlorine and neutralize metals and other additives. Many aquarists swear by Prime by Seachem.You'll also need a test kit to keep an eye on ammonia levels. (Break down and get one instead of going to the aquarium store for testing - you'll need it, at least in the beginning, to get a warning about problems which are developing in the tank and to know when and how much water to change.) After ammonia levels go down, the nitrite level will go up. After that, you'll start seeing nitrates, which means you've got a well-established community of beneficial bacteria. Nitrates only cause problems when they're at very high levels for long periods of time. Keeping the water well-oxygenated is also important, especially while your tank is "cycling" and building its internal ecosystem. You should aim your filter output toward the water surface - that's where oxygen enters the water. This also means being careful of what you spray in the air or use to clean around your tank, as it will enter the water at the surface. Be careful also of how much you are feeding when you've got high ammonia levels.
I would not add a lot of gravel to the tank. If you have more than 3/4 of an inch or so of gravel in the tank, take some out. Goldfish produce a lot of waste and deeper gravel makes it harder to get the gravel vacuumed out and kept clean. Pockets of dangerous gases will collect in stagnant areas of gravel and, when disrupted, can quickly kill your fish. Many goldfish keepers don't even use gravel in their tanks (going "barebottom"). I keep a little in my tank because goldfish like to forage and they seem bored without gravel to play with. While bacteria will make a home in the gravel, they also live on the inside of the aquarium walls, in the water, and in the filter. You can also get a filter which provides "biological" filtration, which means it provides a surface area for bacteria to live on. This part of the filter is usually never changed out and is only occassional rinsed in aquarium water - not straight tap water which will kill-off the bacteria colony.
The sites which were recommended to you are excellent. I'm especially partial to Goldfish Connection. If you go to their site, page-down the left-side menu until you see the "Information" links. You should find all the guidance you need there. It will be a big help in getting a weekly maintenance routine established and helping you to pick-up on potential problems before they get out-of-hand. The site owner is always willing to help if you contact him with questions. Some good forums are available as well: try Goldfish Utopia and Goldfish Paradise, as well as the forum at KoKo's. Search the older messages and you'll find a huge amount on issues similar to your own without having to start new threads. I'd also recommend the book Fancy Goldfish by Johnson and Hess. It contains almost everything you'd want to know about everyday care and disease treatment.
Good Luck!
