Neon Tetras dying off daily

[Taregreen]

S.O.S.! Over the last week my Neon Tetras have been dying off steadily and I can't figure out why. I started with a nice school of about 25 and now I'm down to the last three or four. They're in a 90 gallon planted tank with all community fish, mostly tetras, livebearers, corys, etc. My water parameters have been pretty steady at:

• PH = 7.9 (I know this is a bit high as they like more acidic water, but see the kicker below)
• Nitrates = between ~5 ppm
• Nitrite = 0
• Ammonia = 0
• Hardness = 140-160 (Moderate Hardness)
• KH/Buffer = 55-70 (on the low side, but I don't have big swings in PH)
• Water Temperature 77-78F

Here's the kicker! I have a 45 gallon, planted, community tank with pretty much the same water parameters and my Neons are thriving in there.

I just can't figure it out. They look healthy, too. No visible signs of disease or fungus or parasites. So frustrating. Any help is appreciated. Oh, and yes, I do regular water changes and use Prime to dechlorinate. 

Edited November 11, 2020 by Taregreen

[Daniel]

There have been running discussions of tetras dying on the forum in the past like this:

When did you purchase the neon tetras?

[Patrick M. Bodega Aquatics]

I had the same thing happen a while back. Do they look healthy otherwise? How new are they? It could be parasites. I'd recommend treating them with API General Cure as a preventative.

[Taregreen]

For the most part, I bought them in two batches. They all went through a quarantine period in a separate QT tank and were all treated with the Aquarium Coop med trio. I'd guess I've had them all for about two months now.

[Daniel]

Just now, Taregreen said:

I'd guess I've had them all for about two months now.

Well at least that rules out the problem @Brandy was having.

[Brandy]

1 hour ago, Taregreen said:

For the most part, I bought them in two batches. They all went through a quarantine period in a separate QT tank and were all treated with the Aquarium Coop med trio. I'd guess I've had them all for about two months now.

Is the school in each tank a mix of the 2 batches, or was the healthy school kept separate from the unhealthy one from the beginning? I think mine had some kind of gill fluke type parasite--they would seem to breathe heavily, stop eating, and self isolate right before they died. I treated with Paraclense for the full course, and then I lost one more the same way months later--retreated with paraclense and no more losses since. Cory had a video showing that his 2 batches from the same source shipped just a few weeks apart had dramatically different survival rates. The theory is that they are often wild caught and that impacts their survival rate, but even if not, they possibly come from different breeders.

[cornelius85]

A month ago I got 20 cardinal tetras and 20  rasboras. Today I have 18 rasboras and 17 cardinals. I made my peace with it, there will be losses no matter what we do. In the future if I want a specific number of fish, I'll simply buy a couple more.

Edit: Sorry missread your post  your losses are way too many.

Edited November 10, 2020 by cornelius85

[Taregreen]

@Brandy No, the school in the 45 gallon is completely different batch from the two batches in the 90 gallon. I just must have gotten a couple bad batches. Oh well, the show must go on. Thanks for the advice. 

[Patrick M. Bodega Aquatics]

Like I said before, I made the mistake of buying neon tetras at a local PetSmart and in 2 weeks, I went from 20 tetras to zero. So you are not alone!