Fungus on my Goldfish - HELP

Question
HI Chris. I bought my tank 4weeks ago. It is an AQUA ONE AR-380 with a built in filter and light. ON the front bottom left corner it has 126 aquarium tank written on it.  I have 2 comets and 2 fantails in it. The filter is a powerhead 126/380/600. The PH is 6.8 and the aquarium shop told me that ammonia/nitrate kits are too expensive and not required as long as I change the water regularly. I change my water every week on a Thursday and do 50% each time, sometimes 75%. I have the normal gravel at the bottom 2cms thick   a ship wreck and fake plants.  Also have a long rubber type tube which is my air rock.  Everything was going fine up until 3 days ago when I noticed one of the COMETS had fluffy type stuff on either side of it in the middle area, plus its Dorsal fin was flat and still is.  The 2nd day it got worse and the COMET had the white fluff on it and layed on the bottom of the tank whilst spitting its food out, so I rang the aquarium shop I got it from and they explained my comet had fungus and gave me Aqua Master Fungus cure.  She knew the type of tank I had, and told me to put 5mls of this in my tank. (I am treating all the fish just incase). I did this today and my COMET seems to be swimming a lot more rather than laying on the bottom.  The white flaky pieces are coming off in the water, but still attached to him as well. I've been watching my 4 fish swim around, and noticed the one fan tail there is a little white spot on its tail that wasn't there previously. about the size of a match head.  
Can you help me out with advice please.  am I doing the right things and should I be doing the ammonia/nitrate test every week because it concerns me that every else does, but the aquarium lady said its a waste of money.  thanks for your help..  Janelle

Answer
Hi Janelle;

It would benefit the fish to have ammonia and nitrite test kits on hand. In my opinion it is not a waste of money. Ammonia and nitrite are the first thing to check when your fish have problems. Adding medicine to a troubled system can create more illness. If she had allowed you to test for them, the real problem would have been revealed earlier.

You may find that one or both toxins are elevated because the tank is still in the break-in period. The lesions on the fish are from ammonia and nitrite burns. He is healing from the medication because he developed a secondary infection, but also because the tank is nearing the end of the break-in period and the toxins are probably going down. Unfortunately, the tank may always have trouble with ammonia because it's just too small for goldfish. The AR-380 only holds about 24 liters of water and just one goldfish needs at least about 40 liters (10 gallons). Goldfish are very messy guys that get to be very large. I am not very happy to hear that the fish store lady recommended that size for 4 goldfish, especially in a new tank. If she is experienced in fish keeping, she should know better than that. I'm so sorry you had such horrible advice. Even if you made water changes every day, they can't live in such a small tank together. You will need a 160 liter tank or larger for all four of them.

Here is a good web page about goldfish and their real needs;

http://www.firsttankguide.net/goldfish.php

Here is my web page about new tanks that will explain what has been going on in there;

http://www.xanga.com/Expert_Fish_Help

Let me know if I can help you futher and I hope your little guys will feel better soon.....

At Your Service;
Chris Robbins