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Did I Kill My Fish?

Guest Delta1

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I have had two goldfish for eight years, in a 29 gallon tank. Last night I was doing a partial water change and swapping out filter media as per my usual routine. Both fish were active and curious while I was vacuuming the gravel substrate. By the end of the process, one of the fish was unaffected and remains healthy. The other apparently sustained some injury or an illness was aggravated, because that night he descended to the bottom of the tank and stayed there. Over the next 24 hours he rarely moved and had trouble staying upright, making me think there was something wrong with his swim bladder. He made an effort to eat some flakes in the morning, and moved from time to time. I bought some peas, but by the time I got home he was no longer eating or even opening his mouth very wide. He did burp up a couple small bubbles; I don't know if that's indicative of anything. It seems he died some time in the past hour.

I don't have the skills to do a necropsy, but externally everything looks fine. There are no signs of illness, injury, or long-term stress. What could have caused such a sudden and catastrophic downturn, while leaving the other fish unaffected? Is it possible I poured the water in too quickly and physically injured him? I have always been careful to pour slowly when changing the water, but habit breeds complacency and carelessness. Could he have been hurt by the difference in temperature? The ambient temperature has changed rapidly here, and I may not have matched the water temperatures very well. Could the stress of the water change have aggravated a pre-existing condition, like when humans have strokes or heart attacks?

These two fish are survivors; they lived through newbie mistakes that would make me shudder today. I am very disturbed by what happened over the last 24 hours.

[*]Test Results for the Following:

All test results are for ~16 hours after the water change.

[*]Ammonia Level?

0 - 0.25 ppm (maybe elevated by the sick fish's stress?)

[*]Nitrite Level?


[*]Nitrate level?

10-20 mg/L

[*]Ph Level, Tank (If possible, KH, GH and chloramines)?


[*]Ph Level, Tap (If possible, KH, GH and chloramines)?


[*]Brand of test-kit used and whether strips or drops?

Aquarium Pharmaceuticals, drops

[*]Water temperature?

72 F (probably cooler 24 hours ago)

[*]Tank size (how many gals.) and how long has it been running?

29 gals, four or five years

[*]What is the name and size of the filter(s)?

Marineland Magnum 350 canister with large blue filter and white "micron" filter

[*]How often do you change the water and how much?

About 1/3 every 10 days.

[*]How many fish in the tank and their size?

2, seven inches

[*]What kind of water additives or conditioners?

Top Fin dechlor, teaspoon of salt per 10 gal

[*]What do you feed your fish and how often?

Flakes, twice a day, not soaked but they sink pretty quickly

[*]Any new fish added to the tank?


[*]Any medications added to the tank?

Binox for cloudy eyes about a month ago, should be all gone by now.

[*]Any unusual findings on the fish such as "grains of salt," bloody streaks, frayed fins or fungus?

No, but to be honest my examination was cursory.

[*]Any unusual behavior like staying at the bottom, not eating, etc.?

See above.

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  • Regular Member

By changing the filter media you could have most likely killed off your beneficial bacteria which would have caused a cycle bump. How often do you vacuum the gravel? Any ornaments in the tank? What kind of goldfish are they?

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  • Regular Member

Are you sure you didn't injure the fish with the syphon?

Have you tested your tap water for ammonia? It is strange you have it in such a long established tank

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  • Regular Member

One problem I see is your water changes are not often enough or large enough. So weekly 50% water changes and also goldfish don't need salt. Save that for only if they are sick.

One of thing make sure your not under a boil water advisory. I made a lot of fish sick long ago by changing water when there was a boil advisory in effect. The water was bad for my fish as well.

And one other thing. Goldfish should not be fed flakes. A good quality sinking pellet is best for staple diet and then a variety of other things. (check our the food section.) If you much feed the flakes soak them first and don't use them as the main diet.

I would start with a huge water change. Fasting a couple days and a pea.

Hope he is better soon.

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