03-19-2011, 11:09 AM
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Originally Posted by Andyandsue
Hi everyone. I will start off with some background. This is not my first tank, been fish keeping for years now and have had multiple tanks. I have an established 20 gallon tank that I upgraded from a 12 gallon about 8 months ago and all has been well until the last 2 months or so. Recently I've had fish mysteriously die. One moment they are fine not showing any problems at all, and in the morning I'll come down and look and a random fish will be dead with no signs of injury or disease. A few days to a few weeks later, it's the same thing with no rhyme or reason to which fish or why.
As always the parameters are perfect, all at 0 (API Liquid test). I did a water change last night, and again this morning I have a dead fish, a normally quite hardy long finned golden danio who was fine last night.
Any ideas as to what could make otherwise healthy fish just die? The only thing that comes to mind is a bacterial bloom, and in all honesty the water is ever-so-slightly cloudy since yesterday like there is a bloom hence the water change (going to do another today and leaving the light off) but this has been happening when the water has been perfect, in both looks and chemistry. I thought maybe age, since some of the fish that have died are "old" in a sense that they are more than a year old, some are even 2 years+.
It's like one by one my aquarium is dying off and I am very hesitant to add anybody new until I have this figured out.
I've read this happening. It's suggested that possibly there is something in your tank that is leaking a toxic substance -rocks, wood etc? I don't have any other idea, but someone with more knowledge will probably weigh in.