If I could live my life over again, I would devote it to proving that germs seek their natural habitat — diseased tissue — rather than being the cause of the diseased tissue; e.g. mosquitoes seek the stagnant water, but don't cause the pool to become stagnant. - Rudolph Virchow, Father of Pathology
(media.communities.win)
🧠 Memory Hole 🕳️
A sudden change of environment can also kill fish.
They are finicky. You also aren’t supposed to use tap water, are supposed to add water conditioners, and need to only do partial water changes to keep the healthy bacteria alive.
Not sure if any of that applies to you, but just offering a possible explanation for someone who spends way too much time and money on keeping fish.