Why Do My Fish Keep Dying?

[woolieweena]

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I set this tank up 10 months ago and have just been having no luck with it. The water always tests fine and the temp seems normal etc etc. I don't consider myself a complete newbie, I kept African Cichlids successfully for 7 years. I am just at a complete loss as to what's going on. Any ideas?
Tank size: 300L
pH: 7.6
ammonia: 0
nitrite: 0
nitrate: 5.0
kH: 5
gH: 196
tank temp: 27 degrees celcius

Fish Symptoms (include full description including lesion, color, location, fish behavior): they show no physical signs. They just die.

Volume and Frequency of water changes: every 4 weeks (ish), 1/4 water change using a gravel siphon

Chemical Additives or Media in your tank: standard canister filter. I added "Pimafix" tonight as a desperate measure.

Tank inhabitants: Corydoras, Pleco, Neon Tetras, Sailfin Mollies, a Bumblebee catfish, guppies

Recent additions to your tank (living or decoration): added a Pleco 2 days ago. Added non-glazed terracotta pots for decoration about 3 days ago. 

Exposure to chemicals: none

 

[the_lock_man]

What you don't say is how often the fish are dying, and which species. Neons are often quite iffy in a newly established tank, so that might explain that one, although a 10 month tank would ordinarily be established (ie it's built up its biofilm).
 
It's a difficult one, but one thing is that you've got quite hard water, and most of your fish are softwater fish. From your GH figure, there appears to be a reasonably high amount of dissolved minerals in your water, which your cories, plec, catfish and neons aren't evolved to need - but they still absorb them, and this creates problems, particularly in the kidneys.
 
Mollies, IMO, need slightly brackish water, so this again may explain why you may be having issues with these - do they develop the "shimmies" - they wobble when swimming?
 
Are you having problems with the guppies? 

 

[BaylorPerez]

try to lower your ph to about 7.0-7.3 this may help as well as add a stress reliever to the tank, it should help when adding the fix and as well, do you acclimate them for atleast 15 minutes

 

[woolieweena]

 
What you don't say is how often the fish are dying, and which species. Neons are often quite iffy in a newly established tank, so that might explain that one, although a 10 month tank would ordinarily be established (ie it's built up its biofilm).
 
It's a difficult one, but one thing is that you've got quite hard water, and most of your fish are softwater fish. From your GH figure, there appears to be a reasonably high amount of dissolved minerals in your water, which your cories, plec, catfish and neons aren't evolved to need - but they still absorb them, and this creates problems, particularly in the kidneys.
 
Mollies, IMO, need slightly brackish water, so this again may explain why you may be having issues with these - do they develop the "shimmies" - they wobble when swimming?
 
Are you having problems with the guppies? 
 

Thanks for your reply! Well the fish that die are random...that is what baffles me. The deaths are a little bit spread out too. So for example, I'll loose a guppy one day, then the next day I'll lose two Mollies, then nothing for a week, then something else will die. They don't seem to "shimmy" either. They hang around the top a little?
 
I don't seem to have any problems with the Neons though funnily enough. I did have Dwarf Gourami, but they died too

try to lower your ph to about 7.0-7.3 this may help as well as add a stress reliever to the tank, it should help when adding the fix and as well, do you acclimate them for atleast 15 minutes

Thank you! I will try gradually lowering the PH. I definitely acclimate them for 15-20 mins before the newbies get put in...