Loss of fish

[DGWfish]

I bought 5 zebra danios, 5 harliquin, 5 neon tetra and 2 catfish. They were all out of different tanks at fish shop. Put them at top of tank for 20mins. Then let them loose with my other 5 neon tetras and 2 electric blue rams. All was well. I went back 1 hour later to find danios, harliquins and catfish dead. Checked water all ok. No fighting. temp at 27c. 2 days later all other fish ok. Have been keeping fish for 30 years. Anybody any ideas why!

 

[itiwhetu]

Ammonia spike. Did you test for Ammonia

 

[itiwhetu]

That is seventeen fish added into a stable aquarium.

 

[DGWfish]

As said all water ok!!!

 

[imw]

Itiwhetu, is saying (i think) that adding that many fish in one go might have caused a ammonia spike, it is a lot of fish to add in one go.

 

[GaryE]

A lot of fish going in at once, especially if you made the mistake of dumping the pet store water in, could cause a spike.

I know we're all well trained to say ammonia, and this would be a classic. But the harlequins, danios and catfish died. The neons didn't. Could the light on top of the tank have heated the water and killed their oxygen supply? Rasboras can usually handle very warm, but Corydoras (if those were the cats) and danios don't like hotter water. If the Rasboras were touching the heat source, but the neons weren't...

 

[DGWfish]

Itiwhetu, is saying (i think) that adding that many fish in one go might have caused a ammonia spike, it is a lot of fish to add in one go.

Not Ammonia, was checked before and after