disease of goldies

[aquaboy]

Hello all,
I have a question that i know may or may not be answered on a SW forum,
bbbuuutttt...... my neighbor has or now sadly *had* a tank primarilly consisting of goldfish, or more correctly feeder goldfish, and tetras. Recently three have died in succesion and the two remaining goldfish and 3 tetras are breathing hard. Because i am not a freshwater wizard like SOME, cough..cough..not me..cough, of us are; i am asking if there is ANYONE who has the faintest idea of what this is.
Water Params:

Ammonia- 0
Nitrite- 0
Nitrate-unknown
*** a full water change was done yesterday, so i assume 0 for nitrate but did test nitrite, and can assume ammonia is 0 because it is a well established tank.

I am guessing that it is some sort of disease, and they were treated with melafix before, and recently some salt was added. Please help, because we all know people hate losing a fish; as i did 2 days ago, my beloved lawnmower blenny- Waldo. so i now ask myself "wheres waldo?"

[geekdafied]

Pictures of the fish would help a lot. What do you mean by "full" water change. Changing all of the water kills the good bacteria needed in the tank. Also, how big of a tank are we talking about? Goldfish are one of the nastiest fish you can have, and if he has 2 goldfish left, he must have a had a few. I would put 2 goldfish in a 10g tank, maybe 1 unless you wanna change out the water frequently and over filter.

[aquaboy]

well.... we solved it. i believe it was just lack of o2 in the water, and the 100% water change was more like 80% because she always leaves the gravel with about an inch or 2 of water so that doesn't happen. Oh yeah the goldies are about an 1" to 2". Overgrowing the tank isn't a problem though because she has a pretty large pond to put them in when they get large. Thanks for the concern and willingness to help though! its appreciated.

[aquaboy]

P.S she is getting new filter rated for a larger tank. and she has exatly 2 goldfish and it is a 10 gallon.