Why did my fish die? Help!!!?

[Kylie Anne]

that was a big change, you should be changing 25% every week. the temp change was probably too big. also going from horrible water to clean water. did you remember to add dechlorinator?

when you allow the tank to become dirty, the important things are already WAY too high. fish don't care how dirty the water looks, what matters to fish is the level of ammonia, nitrite, and nitrate.you should keep these from getting high by changing 25% each week instead of a large water change less often.

 

[Herbert]

I just bought a fish tank about a month ago. I changed the water today as it was dirty, using the vacuum hose to remove the dirty water. I did not empty the dirty water completely as the fish were still in the tank. I left 25% of the old water and I begin to fill the tank with fresh water using the water hose. I still had the vacuum hose inside while filling the tank with fresh water to make the water appear more cleaner. The fish appeared to be fine until the fish tank was full again and I noticed some of the fish going into some sort of shock. Trying to jump out it seems. When I turned off the water hose and remove the vacuum hose, I notice that at least 5 of my fish were floating upside down. What did I do wrong? Was it too much pressure? Was the water too warm? Help!!!

 

[hmx_mail]

Changing that much water will not cause your fish to go into shock and die within minutes. Even if changing all that water got rid of a good portion of your beneficial bacteria, it will not ever cause the fish to outright die in seconds. And by the way, the bacteria lives in the filter and gravel and decorations, so changing the water won't remove enough to cause serious harm. Many aquarium books will tell you that it's safe to change up to 75% of the water without issue. If you did uncycle your tank, you'd more likely see your fish become sick with ich or fungus about three weeks later.

In any case, the most likely culprit is too drastic of a temperature change between the water from the hose and the water in the aquarium. If the water was too warm, the fish will kind of look like they're having a seizure and then die within minutes. If it's too cold, they would really just kind of slow down and seem lethargic until things warmed up, so too warm is probably the case. This depends somewhat on the kind of fish you have (some, like angelfish and neon tetras are much more sensitive to temperature changes and may die from the cold, but it wouldn't be within minutes). If chlorine was the culprit the fish would come to the top of the water and gasp for air off the surface. Temperature was it.