Join Date: Apr 2012
Location: Albuquerque, NM
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Re: Fish dying overnight
Thank you for your reply. That's an interesting theory you have. It would be consistent with the zebra danios making it through quarantine but then killing off other species. I purchased them at Petco, so I do not know whether these specimens were wild-caught or farmed.
I looked that the live fish just a few minutes ago and also examined the bodies of the dead ones, but do not see any signs of velvet, copper spots, ich, dropsy, or even stress. Iíve never noticed any fish hiding in a corner, or exhibiting a swim bladder problem, or clinching their gills/fins. Each day they all seem to be contently swimming around, then the next morning something is dead.
The only thing different during the night from the day is this. I run the yeast-method DIY CO2 injection since it is a planted tank. At night the CO2 is discontinued and an air pump hooked up to a bubble wand is used to oxygenate the water. I discount the deaths being caused by asphyxia since Iíve never seen any fish at the tank gasping for air in the morning and donít think the addition of CO2 is killing them. Since the water here is pretty hard, I also canít imagine there being a big swing in pH during the night. Iíve tested the water at several times during the day, using more than one test kit. Iíve also taken water samples to the pet store for testing to make sure my test kits are accurate; all the tests come back pretty much the same.
At this point Iím not sure what to do. I donít like the thoughts of treating the tank with medicine, since I donít know what I should treat for since there are no external signs of disease, I donít want to destroy the biological filtration, the tank is planted, and the tank also has many Melanoides tuberculata snails. I suppose I could put the danios back into the quarantine tank, but Iím not sure what that would accomplish in the long-term.
For now I did a 20% water change and put the carbon back in the filter. I generally run without carbon in the filter so as not to remove the plant fertilizer. Itís never been a problem since I use R/O water and make 10% water changes weekly.