8 Fish Dead. No Idea.

[wake]

6 zebra fish dead. 1 fish still alive breathing very fast and barely moving.
 
 
Fish in 20 gallon tank. Fed twice daily. 
 
Fish have been healthy in tank for 7 months.  All levels checked with masting kit and look great. 
 
About a week ago I had a faulty heater and tank temp spiked to 95.6.  All fish survived. I added two more fish since the spike that also died. 
 
I replaced the heater a couple days ago and it kept the water temp at a constant 78 degrees.  
 
Any ideas what is killing them?  Chemicals from new heater?  Bacteria?  Something to do with 96 degree spike? (ive added more fish since then so that wouldnt make sense.  

 

[cowgirluntamed]

What are the water parameters exactly? Actual numbers are good to know. I could be wrong but it sounds like an ammonia or nitrite spike. Either of those will cause damage to the gills. Are these the only fish in the tank or are there others? What kind of filter do you have and what kind of media do you have in it?

 

[Byron]

I agree, always give us the number for tests so we know exactly what they are.  Different people have differing views on what "look great" may mean.
 
I am assuming from your post that the deaths only occurred after the new fish were added; correct that if in error.  But assuming so, it is possible that the new fish introduced something.  The heat rising to 95 will certainly have an impact on fish (another assumption that "zebra fish" means the zebra danio...?), and likely weakened them, which made them more susceptible to any disease that might have been introduced or already been present without noticeable signs to you.
 
The ammonia/nitrite spike could have occurred after the deaths, but adding two more zebra danio to a 7-month old tank of six (with or without other fish) would not be at all likely to cause either, as the existing bacteria can easily multiply sufficiently with these numbers.  Of course, some other factor may have influenced things too.
 
Byron.

 

[wake]

Ammonia perfect yellow =0
Nitrite perfect light blue = 0 
Nitrate orange = 20-30
 
zebra danios only 
 
The two that were added were from my other tank right next to it.( have 4 tanks with danios) and the danios in the tank that I took the two from are doing perfect.  
 
Levels looked perfect.  I just talked to the fish guy on campus and he says because we didn't rinse the heater(link below) that there could of been some contaminates introduced.  Filter is the hang on the back kind with the bio carb filter inserts that you buy with it.  We have been using those on 3 other tanks and for 7 months they have been great!  
 
We did not rinse the heater, do you think that is it?  
 
 
 http/www.amazon.com/gp/product/B000YADYXG?keywords=fish%20heater&qid=1456954322&ref_=sr_1_5&sr=8-5

 

[Byron]

It is possible that something toxic got in the water from the new heater.  Or in the filter/media if new.  Or on your hands... just throwing out possibles.
 
At the first sign of respiration distress, always do a major water change, meaning at least 50% but 60-75% won't hurt in such cases.

 

[Blough]

Agreed, water changes are definitely a good idea. Unfortunately, I wouldn't be surprised if you lost that last danio as well. 

 

 

[Munroco]

Ammonia perfect yellow =0
Nitrite perfect light blue = 0 
Nitrate orange = 20-30
 
zebra danios only 
 
The two that were added were from my other tank right next to it.( have 4 tanks with danios) and the danios in the tank that I took the two from are doing perfect.  
 
Levels looked perfect.  I just talked to the fish guy on campus and he says because we didn't rinse the heater(link below) that there could of been some contaminates introduced.  Filter is the hang on the back kind with the bio carb filter inserts that you buy with it.  We have been using those on 3 other tanks and for 7 months they have been great!  
 
We did not rinse the heater, do you think that is it?  
 
 
 http/www.amazon.com/gp/product/B000YADYXG?keywords=fish%20heater&qid=1456954322&ref_=sr_1_5&sr=8-5

I think he is shifting any possible blame. I've never heard of a new heater contaminating a fish tank, though I suppose its just about within the bounds of possibility.