[Rnasty]

I have a 15 gallon that I just have a few white cloud minnows in and they've been there for a couple years, I just took in a few unwanted guppies and within 1 week they all died. The white clouds are as fine as ever. I tested the water and everything came out fine, water temp is 78.

I'm a little baffled as to what could have killed them, I've kept plenty of guppies in the past and have found them tough as nails. There were no signs of parasites or other afflictions or nipping from the minnows, I just woke up one day and one had clamped fins and was wobbling, in the coming days the same thing happened to the other guppies.

Any thoughts?

 

[Mark Fisher]

No ammonia spike from the increase in bioload?

 

[Rnasty]

Not that I recorded, and I do regular water changes. One of the guppies came from a neglected tank but the other two came from separate healthy tanks

 

[ichthyogeek]

Define "fine"? Like, what were the actual parameters?

My instincts are screaming "it's old tank syndrome" or "it's livebearer disease". Especially since you mentioned clamped fins and wobbling.

 

[Rnasty]

0 ammonia, 0 nitrite, 30 nitrate. My water here is high in nitrates but is stable at 30ppm

 

[ichthyogeek]

30 ppm seems kind of high for a fish tank... Also what temperature was the tank? Were you able to measure the hardness of the water?

 

[ElleDee]

Is 30 ppm high? I thought for freshwater fish maintaining it under 40 was fine?

Fyi, the EPA standards for tap water is 10 ppm. If you are way over you might consider not drinking it, especially if you have vulnerable people in your household.

 

[kozlany]

Hopefully you didn't introduce a disease into your tank. Columnaris comes to mind and guppies especially female guppies tend to succumb quickly.

If the tank water they came from was considerably different from yours it could just be failure to adjust. While most guppies are fairly forgiving some especially older fish might take the change hard.

I'd also be wary of water that is 30 ppm out of the tap. Makes you wonder what else is getting in to the water.