# Fish suddenly dying ?after new filter added



## Nickib (Mar 6, 2012)

My 1st post so excuse any mistakes! We have had a tropical tank for over 2 years and have managed to overcome most problems by searching Internet forums such as these but I'm at a loss as to what's happened. 

We have a 64l tank, not planted and up to 3 months ago kept 4 mollies, 2 swordtails and 3 tetras (so I wouldn't say overstocked). The trouble came when 1 of the swordtails became sick 3 months ago. Sorry, I can't remember details but I added some methylene blue to try and save it but measured it wrong and the tank went black :-( I did frequent large water changes initially but lost both swordtails and a molly (the Molly had looked not right for about 12 months though) My filter also stopped working. 

Unfortunately, around this time I slipped a disc in my back and water changes had to become less frequent and I couldn't bend and twist to change the filter. Even so, we noticed a baby Molly in the tank about a month ago which I took to be a good sign!

Last week I did another water change (approx 30%) and bought a new filter. Everything seemed fine in the tank, no signs of illness and looking less blue but I got up this morning to find 2 of the mollies dead. I've tested the water and parameters are absolutely fine. Surviving fish look ok but I'm very sad and worried that I've harmed the fish in some way. 

Any thoughts or ideas of what might be going on?


----------



## GwenInNM (Feb 2, 2011)

Nickib said:


> My 1st post so excuse any mistakes! We have had a tropical tank for over 2 years and have managed to overcome most problems by searching Internet forums such as these but I'm at a loss as to what's happened.
> 
> We have a 64l tank, not planted and up to 3 months ago kept 4 mollies, 2 swordtails and 3 tetras (so I wouldn't say overstocked). The trouble came when 1 of the swordtails became sick 3 months ago. Sorry, I can't remember details but I added some methylene blue to try and save it but measured it wrong and the tank went black :-( I did frequent large water changes initially but lost both swordtails and a molly (the Molly had looked not right for about 12 months though) My filter also stopped working.
> 
> ...


Welcome to the site! If you didn't keep any of the existing filter media, you would have gotten rid of good bacteria that may have created a mini-cycle, but with such a small number of fish in a large tank, I'm not sure about that. What are the actual readings on your ammonia, nitrite and nitrate? An ammonia spike could have killed your fish. Wishing you a speedy recovery with the back, ouch 

Gwen


----------



## Nickib (Mar 6, 2012)

I have been testing the water with some test sticks but they don't measure ammonia!! Nitrites are 1 and nitrates are 25mg/l both of which say a safe reading. I still have the old filters drying out in a bucket - is it too late to put them back in?


----------



## GwenInNM (Feb 2, 2011)

Nickib said:


> I have been testing the water with some test sticks but they don't measure ammonia!! Nitrites are 1 and nitrates are 25mg/l both of which say a safe reading. I still have the old filters drying out in a bucket - is it too late to put them back in?



Test sticks are not reliable. Any nitrites are deadly for fish, so that may have been what killed them. Bacteria can live until it's completely dried out, and perhaps even shortly after that, so you may want to put that back in. Since you have a reading of nitrates (20ppm is considered acceptable) it's strange you'd have nitrites. Something is way off balance. Do more frequent water changes, to keep your water quality up to par. Use Prime as your product to condition and remove chlorine from the tap water

Gwen


----------

