Did 40% Water Change Then Next Morning Nearly All Fish Are Dead?

[Ethan040]

Hi guys, yesterday i did a 40% water change i do a 40% water change every 2 weeks i leave it 2 weeks because when i was doing weekly changes i was getting terrible hair algae i have been doing this for 8 months now and the fish have been perfect i have never had any problems with this tank or any of the fish in it but today i woke up to find all but my corys and bristlenose dead, while doing the waterchange i moved some sand about as the filter pushes it to one corner of the tank and i moved a few rocks about to clean under which i had not done in a few weeks.

I tested the water when i found them dead and my nitrites where 1.0 and ammonia 0.50 nitrate 40 all tests done with a API master test kit.

Ive done a full water change then left the tank to come to temp and settle and my readings now are nitrite 0.25 ammonia 0.00 and ive not tested the nitrates yet

Fish in the tank where..

3 sterbai cory
5 blue spotted cory
1 Bristlenose
1 molly
5 black skirt tetra
1 SAE

All are dead except the corys and BN no skin flaking off no sores no signs of any disease at all and the corys and BN are fine there like nothing has happened even after moving them to my spare tank.

Any ideas what has happened? Thanks

 

[the biffster]

what dechlorinator did you use
did you match temp

 

[Ethan040]

I used API stress coat its not what i usually buy but when i got my new tank i got a huge tub of it, it was unopened and is still in date, i have been using it for around 8 months i use a little bit more then stated though but i always do to make sure.

EDIT: i did not match the temp no i just use cold water, ive read some threads on this ages ago and alo of people where doing it and i always have with no harm done to the fish.

 

[Curiosity101]

I imagine it's likely that there has been some work done on your water line. Or possibly that someone has used your water change bucket (if you use a bucket?) for something since your last water change.

 

[Ethan040]

I did a large water change on my other tank and that's perfect i did another today on it also when i nicked some media from it for my spare tank for the corys and BN, that tank has corys and neon tetras in it, i used the same water same tap and same API stress coat.

The spare tank the corys and BN are in has the same water and conditioner in also and they have been fine since moving them.

Thanks

EDIT: also nobody uses my bucket but me i know that for sure and i use the same bucket for all my tanks.

 

[Curiosity101]

Did you do the change on the other tank first? Or on this one first?

 

[Ethan040]

I changed the now bad one first.

Thanks

EDIT: i have just tested the spare/hospital tank and it is giving the same readings as the bad tank 0.00 ammonia and 0.25 nitrites.

Also my tank is 180litres

 

[Curiosity101]

So there is a chance there was something in the pipes that the first tank got... that the second one didn't?

 

[Ethan040]

Maybe yeah i hope not, its never happened before though, hope it does not again.

Thanks

 

[Timmy_Bee]

did you add the dechlor to the tank? or the bucket before adding to the tank?

The only other thing i could think of is that nasty pockets of gas can build up in sand substrate, and maybe you disturbed one that killed your fish?
Might be good practice to at least move some sand about more often than every two weeks.

 

[mbsqw1d]

are u uk based as the cold water these days is very cold! if u didnt add any hot water then that would have been a huge shock to some fish.. however most catfish are ok with an influx of cold water.

 

[-Craig-]

are u uk based as the cold water these days is very cold! if u didnt add any hot water then that would have been a huge shock to some fish.. however most catfish are ok with an influx of cold water.

I'm in the UK too and the water is very cold in the taps.

But i think it would be a Gas build up you disturbed or something.

 

[mbsqw1d]

are u uk based as the cold water these days is very cold! if u didnt add any hot water then that would have been a huge shock to some fish.. however most catfish are ok with an influx of cold water.

I'm in the UK too and the water is very cold in the taps.

But i think it would be a Gas build up you disturbed or something.

gas build up? if the substrate has been disturbed and detrius has been allowed to surface then an ammonia and phosphate spike might occur..