Right now I am so disappointed I don't know where to start. About 6 weeks ago i set up a 100 gal tank, let it cycle for about 10 days, put in 5 small goldfish, a week later i put in 3 of my larger goldfish that i have had for 5 or 6 years that i put in our pond in the summer and tank in the winter. I also added 2 black mollies and 2 redcap orandas that i bought a the pet store. Everything looked fine all seemed to getting along good. About a week ago 1 of the redcaps went missing i looked all over for it but thought it got ate up by the others. Yesterday i went to check on my tank and could not believe what i saw, my largest goldfish was covered with a whitish film, his lovely tail was almost gone, reduced to strings, the other 2 larger goldfish and the black mollies could not be seen. Tested my water NH3 was not an issue but my nitrates were off the scale. My first though was decay and i started tearing everything out of my tank and found stuck under and in a large plastic plant 2 goldfish, 2 mollies, and the 1st missing redcap. I did a 1/2 water change and nitrates are way down and i will " now " keep checking it. The question i have did 1 little fish { about 1 inch long } start this chain reaction or am is there something else going on that i should check into. Any and all help would be appreciated.

Down in the Dumps---Al

One hidden dead fish can do this especially when others die and are unfindable/unnoticed, ammonia spikes like crazy, nitrates will skyrocket, fish will gasp at the surface, swim odd then die.

this seems to be what happened, there was also a brownish algae {?} starting on the glass and rocks, I washed and wiped it all off, Should i do another water change? I am at a loss of what to do next. Have never had such a problem.
Al

Also removed the plastic plants that the dead fish were in. Don't know if they got stuck in there or got sick 1st and swam into it to die.

Al

So sorry to hear about your fish Al. One fish dying and decaying in a tank can definitely set off a chain reaction resulting from the initial ammonia spike. I'd do some more water changes before you restock and test your water frequently. Don't be discouraged; just take it slow and make sure your water is back to normal before adding anything else. Did that one goldy make it?

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When in doubt, do a water change.

Thanks for the replies, i am going to do another 25 % water change today.
My oldie Goldie is still hanging in there and it is puzzling the 5 small goldfish don't seem to be in trouble at all. My initial tank fill was with town tap water, but i am going back to RO that i have used in my smaller tank. Any other help or comments are welcome

Al

i am also very sorry to hear about your fish loss. like whitedevil said, it can deffently start from a small fish that can go missing. thats why it is ALWAYS important to check water conditions and qualities. you have to remember that in a natural environment, a "missing" fish in a huge lake/stream/etc. will simply decay and what not. but this is in an enclosed area...

my .02

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Calling aquariums and fish boring is like calling a hott model ugly.

http://www.aquariumforum.com/f2/save...fish-2930.html

I lost some very rare to my area fish to an 8.0+ ammonia spike about 6 months ago. decaying "missing" fish in my sand, I had to start over.

Yeah, that assumption of the missing fish being eaten cost me dearly, a mistake i won't soon forget. never too old to learn something new.