Its lead me to the point where I don't wanna spend more money on the fish I've kept as a kid because in her care they don't seem to.do as well as they did with me as a child. I was able to keep tetras barbs n betas for years now I cant keep them a month.
Tap water has changed a great deal over the last 20+ years and water that what was safe back in the 70s is now toxic to anything that ingests it.
You live in the US and probably have chloramine in your tap water now. Did you use a dechlorinator that neutralises chloramine?
How long were the fish in the new tank before they died?
Have you tested the tank water for ammonia, nitrite, nitrate and pH?
What sort of fish did you get (that died)?
What symptoms did the fish have?
Are any fish still alive in that tank?
Do you have any pictures or video of the dead fish or the remaining ones?
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You don't do a 100% water change unless something extremely poisonous is in the water, then it's easier to get the fish out and put them in clean water.
If you have an ammonia or nitrite reading above 0ppm, do a 75% water change and gravel clean the substrate every day until the levels are back to 0ppm.
