Fish shocked/dying after water change!

[Si_2202]

HI all,

I've just done a 50% water change in my 500l tank and all my Rummynose Tetras ended up laying on the substrate. The rainbows and SAE seem to be unaffected. Some of the Tetras are up and swimming around again whilst others are still on the substrate not moving, seemingly dead.

I've never experienced anything like this before so any help would be appreciated!

Edit: The tank has been running pressurised CO2 for approximately 2 weeks now. It's filtered by a Eheim 2217 and a Fluval FX6. The water I put in was about the same temperature as the tank and I dechlorinated the whole tank before putting the filters and heaters back on.

 

[castle]

Did you treat the water for chlorine and chloramine?

Turn on any aeration you can in the tank for start, most fish can handle a few degrees drop, but did you add really cold water to a 25℃ tank? that'll stress 'em.

And your edit, answered these questions!

 

[Si_2202]

I filled it from the tap with a mix of hot and cold to approximate the correct temperature. According to the thermometer the tank is at the same temp now as before the water change. I treated the whole tank for chlorine once it was refilled and before I put the filters back on.

I've netted a couple of the ones I thought were dying and their gills are still moving so I assume they're just shocked, more have recovered since I posted the first message.

I've just noticed the CO2 came on whilst I was doing the water change. It's attached to the outlet of one of the filters. Is it possible that when I turned the filter on, there was a massive buildup of CO2 released into the tank and it gassed the fish?

I've turned the CO2 off for now and pointed the filter outlets at the surface to aid gas exchange.

 

[MirandaB]

Rummynose can sensitive to varying water conditions,are you using tap water?

oops posted at the same time.

 

[G H Nelson]

Temperature was similar....so could be a excess of chlorine and chloramine or heavy metals!
Try adding more water conditioner!
hoggie

 

[Si_2202]

Rummynose can sensitive to varying water conditions,are you using tap water?

oops posted at the same time.

Yes, I've been doing water changes in this tank the same way for a couple of years. The only other thing I can think of apart from gassing them is that the tap water could have been significantly higher in ph than the tank now it's running CO2. I *think* all the Rummy's have recovered now, although they're all hiding in the corner.

Temperature was similar....so could be a excess of chlorine and chloramine or heavy metals!
Try adding more water conditioner!
hoggie

That's possible, My water comes from a well as I'm on a farm. I've tested for Chlorine before and there wasn't any but heavy metals are another matter. I've added a load more water conditioner just in case

 

[ian_m]

You put water conditioner in the tank before adding tap water, not after.

 

[Si_2202]

You put water conditioner in the tank before adding tap water, not after.

I've done it this way since I've had the tank, which doesn't make it the right way to do it I know, but it hasn't caused issues to date.

EDIT - I just wanted to clarify this point for anyone who might come across this thread later. My water comes from a well so doesn't contain chlorine. I'm 99% certain I don't need to use water conditioner but I do add it just as a safety net, hence my rather blase attitude towards it.

 

[sciencefiction]

Yes, I've been doing water changes in this tank the same way for a couple of years. The only other thing I can think of apart from gassing them is that the tap water could have been significantly higher in ph than the tank now it's running CO2. I *think* all the Rummy's have recovered now, although they're all hiding in the corner.

My guess is you've gassed the fish with CO2. As for the pH difference, it plays no part whatsoever. pH change due to injected CO2 plays no role on water chemistry that can affect fish. It is actually the CO2 itself that is toxic...

I've just noticed the CO2 came on whilst I was doing the water change.

It is possible your well water was already saturated with CO2(my tap is) and the extra you were injecting during the water change, plus the smaller water volume, has tipped things in the wrong direction. Certain species of fish have lower tolerance for CO2 concentration than others, which explains why some got knocked over and others didn't.

 

[Aqua360]

Rummynose are well known for lying on their sides and sometimes dying through shock, I'd venture to go against the grain and ask if you did anything differently like move ornaments and whatnot, rather than water chemistry