New Fish Dying

[robbee]

Have had a successfull well established 180litre tank for several years. Recently put 3 new black neons into the tank. All died withing 3 days.Added one further black neon which also died within 2 days. All the rest of the fish in the tank are ok. Water quality re ammonia ,nitrite and nitrate is excellent and temperature stable at 24 deg. Fish came from my usual supplier and he informs me he has had no other problems with this batch of fish. Only possible reason I have come up with relates to my having removed an extra internal filter (which I didn't need anyway) and this may have impacted on the oxygen in the water. The black neons did seem to have rapid gill movement? If it is an oxygen related problem, why are the other fish ok.

 

[Bobtastic]

You say that the Ammonia, Nitrites and Nitrates are "excellent" but don't give any numbers. People really need to see figures and reading to give proper advice. Also you've not mentioned pH, as that can have an effect on fish.

If you haven't got it already try and point/angle the filter outlet towards the surface to agitate the water, that will help with oxygen exchange.

 

[robbee]

You say that the Ammonia, Nitrites and Nitrates are "excellent" but don't give any numbers. People really need to see figures and reading to give proper advice. Also you've not mentioned pH, as that can have an effect on fish.

If you haven't got it already try and point/angle the filter outlet towards the surface to agitate the water, that will help with oxygen exchange.

Ammonia and nitrite both nil. Nitrate also very low 5-10mg/l (this has been tested using both my kit and by my fish supplier). Ph value is approx 7.1.
Filter outlet is agitating surface and I have introduced more areation with an additional pump and airstone. Only other thing I can think of is stress due to what appears to be quite a temperature differential between my tank 24deg and my suppliers water which is definitely colder. Have taken care when intoducing new fish and doing it slowly by equalising water temperatures and only introducing tank water to the transit bag gradually. Problem seems to something which existing fish can handle or are used to, whilst new fish are being shocked!!