suddenly everyone seems sick

Question
QUESTION: Hi.

I have a ten gallon of 6 platys that has been set up since late July.  Water levels have been good in terms of ammonia, nitates, nitrites, etc.  Near zero by the dip sticks reading.

I got two corys to add this weekend.  I noticed this evening they look horrible.  Actually I am certain they wont make it through the night, the are floating up and getting caught on the siphon tube and everything.

The platys also dont look great (they were great before!). Two are swimming around fine but the other 4 are up in the corners.  One looks like he is arching his tail up almost.

I do know the temp went down in the aquarium by about 4 degrees since the room temp has dropped drastically.  I have the heater on to gradually bring it back up (it is down to 74 was at 78).

What on earth could be going on!?  Should I do a water change?  I have been doing a 25% water change every 1.5-2 weeeks anyway but can do one now if it will help save anyone in this tank (its been about 1 week since the last one).

Thanks in advance!

ANSWER: Hi Kerry,
I'd definitely do a water change. Poor water quality is definitely one of the first things to suspect when your fish are dying or acting sickly.

Have you tested your water? Its always possible there may be ammonia or nitrites present. You never know.

Try doing 50% water changes daily. That's what I'd do if this were my tank.

Best of luck and I hope all goes well!
Karen~

---------- FOLLOW-UP ----------

QUESTION: Hi Karen,

Sad update.  Within 24 hours everyone is dead.  It was like a white fungus ate them alive.  It was so quick, I dont even get what happened.  

When I got home today at 3 there were two alive, but with white starting to get them, too.  I added some aquarium salt (this was before I got your response to change 50%). But things just kept declining.  Like I said, such a fast attack of this white stuff.  I Never woul dhave brought the 2 catfish in on Sat if I thought anyone was sick.

When I tested the water, nothing was elevated (ammonia, nitrites, nitrates, etc).

What can I do to this tank now to get it back to where it should be to "start over"?

Thanks again.
Kerry  

Answer
Hi Kerry,
Oh I'm sorry...

Were they covered in the white fungus before they died? Or after? If after, then that's common...A nasty old fungus develops on fish that have passed away almost every time. But this is especially common in aquariums that have a lot of waste in the gravel, which really encourages its growth.

I'm still not 100% certain to say that "this or this" happened. Its a strange thing. If your ammonia and nitrites tested out 0 then it must have been a fast acting illnesses. The cories may have brought it in even if they didn't show symptoms. Probably the best thing would be to quarantine any new fish in a separate tank before adding them to your main aquarium.


If this were my tank. I'd start over by changing about 50% of the water and perhaps repeat it again the next day. Clean the gravel very well. I don't think its necessary to do a complete tank tear down. Just after the thorough water changes, let the tank run empty for several days. If you feel everything is good. I'd add a few inexpensive fish like 3-4 zebra danios and see how well they do after a week or so in the tank. If all is well, then you can move on from there and carefully re-stock it. Try to have a quarantine tank on hand to put any additional new fish in for at least 12-14 days.

I hope this helps and best of luck!
Karen~