All Fish Apart From Three Tetra Dead :(

[chinapatterns]

Hi guys,
 
I'm new to most of this so please bear with me whilst I give you some history.
 
September 2012 I got a new tank, my first. 30l  After doing lots of reading I purchased some docor liquid api testing kits and started a fishless cycle.    After cycling the tank for four weeks I purchased two male molly's.  Both of theses did well but I had some issues with bullying and a week laterone of the molly's had to be returned to to the pet shop.  I replaced the molly with two female guppies and everyone was happy.  The tank was fine and stayed that way until the start of January.
 
I didn't want to add more fish to the existing tank so decided to upgrade to a 60l  - I used the cermanic media / water and filter from the original tank and topped it up with new water (so aprox a 60% water change) The fish were put in to the new tank and everything seemed fine.   I waited a few weeks checking levels and as everything was fine decided to introduce some more fish - this is were it all went wrong!
 
I put in one small male guppie and 6x neon tetras, the following week one of the female guppies died, the week after the other female guppie, male guppie, a few days later the male molly and a few days after that three of the neon tetras.
 
The guppies appeared to have tunred white when they died, the tetras appear to have the ends of their tails rotted away ( if that makes sense)
 
I still have three fish who are alive but the water now looks very yellow/green - it has always been clear before. 
 
Amonia has rocketed out of nowhere but i assume that's due to the dead fish.
 
Where do I go from here?  Start again do a 90% water change?    upset any help would be appreciated.
 
 

 

[fluttermoth]

Big water changes, making sure the new water is warmed and dechlorinated, until you get the ammonia (and nitrite) down to zero.
 
Then continue to test daily and water change if necessary, until both ammonia and nitrite are at zero without needing to water change.
 
I'm guessing that your new fish overloaded your filter bacteria. You should never increase your stock by more than 50% (so, if you had six guppies, you could add no more than three).

 

[chinapatterns]

Ahhh, added 7 small fish to three large exisitng ones so thought the rule was more to do with size etc.  Lesson learnt.  should I change the filter just in case?  It's a biorb 60l

 

[fluttermoth]

Gosh, no!
 
The filter is where all your good bacteria live (always assuming that you haven't been killing them off with washing in tap water, or changing it frequently). You need those bacteria; they're the ones that 'eat' the ammonia and keep your fish safe.
 
Never replace anything in your filter, apart from carbon/charcoal (and that's better off being replaced with more sponge or ceramics). Just rinse it off in some old tank water, when you do your water changes, to stop it getting clogged up.

 

[chinapatterns]

No, I havent been washing in tap water etc, havent touched it aside form changing it from one tank to the other and always use aqua safe before adding water into the tank and leave it out for a bit so it's not too cold.  Cleaning the tank out at the moment but can not find the other dead tetra.
 
Should i remove the media into some tank water to see if i can find it as that's bound to cause another spike I would assume if left in there somewhere.
 
 

 

[fluttermoth]

It would be best if you could find it yes; just don't let the media dry out.
 
And if you can't find it, try not to worry; it's very common not to be able to find dead fish; just keep your eye on the ammonia level and water change if it goes up.

 

[chinapatterns]

Thanks fluttermoth,
 
Searched the tank and no dead fish to be found although I did find a partial on one of the plants so I'm assuming they have decomposed after death.  Done an 80% water change and just waiting for the temp to come back up in the tank before i re-introduce the tetra's 3.  The water looks a lot better now.  Kept the media in old tank water and have not touched the filter so fingers crossed. 
 
Will keep the tank at the current three tetra level for the time being and see how we go for 6 weeks or so and then only add one new fish at a time and "monitor monitor monitor"
 
Thanks for your help.  Will have a look round here for some more hints and tips.

 

[fluttermoth]

You're very welcome
 
Hope you manage to pull them through.