Zebra Danio Death Linked To High Ph

[fish_4_life]

Hi All,
I have had 8 Zebra danios in a 3 foot tank for about 14 months, I mow only have two the latest fish to die was about an hour ago, The same thing has happened each time, the zebra danio will start getting really fat as if full of eggs, then over a space of a month or two will overnight develop swimbladder it seems like and will be dead with a couple of hours after this, I treat them with swim bladder but the fish die within hours still, this has happened to 6 of them over 14 months I have two left one is really big like the ones that died and one is really slim line. my water tests are all 0, apart from my PH which has always been in the highs of around 7.8 any ideas as I would like the last two not to die
 
Many Thanks 
 
Dan 

 

[the_lock_man]

Hmmm. Interesting one.
 
2 things spring to mind as possible causes.
 
1) It may be the delayed effects of ammonia poisoning, if they were subjected to a fish-in cycle that allowed the ammonia level to go quite high. Ammonia poisoning is quite like smoking in humans - the health issues often don't emerge straight away.
2) It may be water quality issues. I know you say you have 0s, but if that includes nitrate, then something is wrong. How often do you carry out water changes?

 

[fish_4_life]

Hi the_lock_man 
 
I do a 25% water change every week and an half, I test my water every week and I've never had the ammonia levels go above 0.2 all my other fish have always been fine, 
 
I have 2 harlequins, 4 albino corydorys, 12 tank bred guppies, and a rubber nose plec and 3 glass catfish.
 
I have an external filter as well so The water quality shouldn't be bad
 
Dan

 

[Blondielovesfish]

I don't think your pH would be the cause of this, unless it has recently spiked/fluctuates a lot.

Google "Dropsy" and see if they look anything like that.

It may be that they became egg bound but fail to drop the eggs. However, if they're normally stream lined, then it won't be the case of eggs. (Males are stream lined while females are a bit plumper)

Also, with your other fish, all of them (except the Rubber Nose Pleco and Guppys) need schools of at least 6.
Depending on the actual size of the tank, it may be over stocked as well

 

[N0body Of The Goat]

Hi the_lock_man 
 
I do a 25% water change every week and an half, I test my water every week and I've never had the ammonia levels go above 0.2 all my other fish have always been fine, 
 
I have 2 harlequins, 4 albino corydorys, 12 tank bred guppies, and a rubber nose plec and 3 glass catfish.
 
I have an external filter as well so The water quality shouldn't be bad
 
Dan

25% every ~10 days is quite low, I do ~50% on each of my 6 active tanks every week. Your nitrates could be quite high (this is linked in with water quality).
 
What temp are you keeping the tank at? Zebra Danios should typically be in a heaterless tank that spends most of the year between 18C and 20C, if they are usually in warmer water than that they will have shortened lives through higher metabolic rate.
 
I would start with a ~75% water change ASAP and then get into a habit of more frequent, larger changes.