Unexplained deaths! Please help.

[Spandex]

On Saturday I stripped down my 140 litre tropical freshwater tank to move all the inhabitants and the filter etc to a new 210 litre set up. The whole move was completed within an hour and all the old tank water saved. All seemed well until the next day when I noticed all the fish breathing very heavily. Within an hour or so they were all hanging at the surface. I did a 40% water change and they seemed much better. Temperature is a steady 25 degrees. I tested the water and ammonia and nitrite are zero and nitrate obviously present but relatively low. It seems every time I do a large water change they improve for a few hours and then deteriorate again. During the night 2/3 of the inhabitants have died. The only thing that has changed is the addition of a 3D rock background made specially for aquariums out of fish safe resin and fibre glass. I have noticed the water smells like the background did when I unwrapped it – a chemical ‘new magazine’ kind of smell and this is making me suspect the background may be affecting the water – has anyone else experienced this? I removed the background last night and did a big water change, I still woke up to many dead fish, but now I don’t know whether this is because they were so damaged already it was too late or whether the background has nothing to do with it and it is something else!?

My only other suspicion is that the new tank is in a flat and perhaps the tap water is treated in some way – I know it is run through a special coil to remove some of the hardness but the hardness tests come out fine. Any ideas from anyone greatly appreciated,

Thanks

 

[dkpate]

I would say it was probably the chemicals in the new background. I lost one of my favorite fish because I didn't let some silicone cure long enough. He died about 2 weeks after exposure.
Since you say the fish seem fine right after a water change, I am wondering if they don't have enough oxygen. That would cause the gasping, and the normalcy after the water change. When you pour new water into the tank, it creates oxygen by agitating the water. Try lowering the water level so the filter water splashes, or adding an air stone.

 

[Spandex]

Hi Darby

Thanks for your reply. I already have the tank water at a level that achieves maximum water surface area and the return from the filter is via a spray bar which is agitating the surface. When I got home last night all the remaining fish look much better and the smell has gone. The water changes must have just been temporarily diluting whatever toxin was leaching out of the background. I am now certain that the problem is that background and I will be making a complaint to the shop I bought it from. I lost a lovely angelfish to this amongst other things and the whole experience has been pretty horrible!

Thanks for your help

Spandex

 

[dkpate]

I am glad the fish are doing better! I hope you give the pet shop a piece of your mind, and maybe send an e-mail to the manufacturer of the background.