Danio fine to dead in 7 hours(?)

[cmedalis]

My 10 gal has been up and is at the very end of it's cycle, afaik. Last nite after cleaning up my QT tank, I did my usual inspection of this tank, which is inhabited by 1 Comet goldfish, and 2 gold zebra danios. They were active as normal, zipping around the tank, and coming to the top at one corner (where they get fed). They only get fed once a day (at noon-ish), and get regular water changes (20% weekly), with some extras (15%) every other day because the danios are new introductions, and I expect an ammonia spike.
Today I woke up to find one of the danios was swimming askew. Unable to maintain attitude, twirling about the long axis, and it looks as though it is partially paralyzed on one side. Also, the gill covers show bright red color.
I removed this fish to a small bucket with fresh water, and tested the tank water:

ph: 7.8
Ammonia/Ammonium: .25 mg/L
Nitrite: ~ .3 mg/L
Nitrate: ~ 5.0 mg/L
Temp: ~ 74 deg F

When I left for work this afternoon, the fish was all but dead, and if it does die, I may be able to inspect it further for a cause, but what should I look for? Other than the irregular swimming, and coloration, there were no external signs of disease, and less than 8 hours earlier, it was doing quite well.

I am worried that some strange disease has infected my tank, and I will have to start all over again.

 

[Allivymar]

It could be disease; how long have the danios been in there?

I kinda put my money on the ammonia/nitrite levels tho.

If you going to actually autopsy it, you can get some info about that here: http://216.239.37.104/search?q=cach.../akcanecropsy.doc+fish+autopsy&hl=en&ie=UTF-8

 

[cmedalis]

you would think so, but these levels rarely change. I have 2 known spikes, one when the goldfish had ICH, and the meds probably killed off the nascent bacteria colony. Since then the levels have been dropping to a steady reading, which never seems to change. I have a feeling that my kit may be reading wrong, or I am reading it wrong
Anyhow, the danios have been in the tank since Saturday (Nov. 1). And they have been getting water changes frequently.
Which is why I question my test kit, as I changed water Monday (Nov. 3rd) in the evening, and on Tuesday at noon, the numbers hadn't changed. :?

What am I doing wrong here?
Should I just make the investment in some Bio-Spira, to give a boost to my bio-wheel?

 

[cmedalis]

well even before the advice is give, i am doing it. I got home from work ,and as usual, I vacuumed out the QT tank, and did a small water change. But I also did a water change/ vacuum of the 10. I will run some water tests on it as soon as things settle down. Any one else have problems of water looking a bit cloudy after a vacuum of the gravel??
I did do a quick inspection of the dead fish, no obvious signs of parasites, or infections. No necrotic tissues, no gross signs of infection, either. If it was the water, I will do what I can to get it right. It's that d*** goldfish! He is making a mess of things
He really needs his own tank i think. Ok off to test water. THanks all, you've ben a great help Cheers.

 

[Sati]

Any one else have problems of water looking a bit cloudy after a vacuum of the gravel??

Sure, it always stirs things up a bit routing around in the gravel :]

 

[cmedalis]

Yeah, that is what I had figured.
Even after I did the water change, my test kit still shows positive for ammonia. :x
Any one have a reccomendation of a test that is more accurate? My current test is from the Tetra Laborette, and it tests in .25mg/L increments, from 0.0 thru 1.5.
I'd like to get something that can test in say .1mg/L increments, from maybe 0.0 thru 0.5, because if ammonia is still a problem, I can do more frequent water changes, or add something (ammo-lock, zeolite chips, whatever) but I'd like to be able to see the end results.
Thanks all.