Fish dying for no apparent reason, what gives?

There should be enough oxygen still in the water at night, considering the plants produce it all day. The CO2 won't drive the oxygen out of the water.

Have you been testing for ph fluctuations during lights on/off?
 
thebach said:
2 were new, 3 others were not. If one more dies I will take back Cat. Would a Pictus Cat kill fish as big as they are? I have never heard they attack and kill fish as large as they are. Plus no marks on fish at all. If my plants are not giving off oxygen at night, and I have c02 going, why would I not run out of oxygen? There is no airstone going, and no surface agitation, so where would my tank get oxygen at night?
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remember thebach, the people here are only sharing their wisdom and advice, it is up to you to asses the information and act according to what you think is right. Good luck, my brother...
 
well most of the posts are saying I don't have enough o2 in the water at night. If it was my cat why did he wait months to start killing fish as big as he is. I hooked up an airstone for the night, I will see what happens now, any more die this way I will get rid of Cat. But there is only circumstantial evidence against him. I wish this was a more obvious question where everybody was telling me the same thing. :(
 
One more suggestion. Turn the lights off but leave a nightlight on an extension cord shining into your tank. Try checking in after lights have been off for a while. If It's oxygen defeciancy they should show signs.

good luck
 
thebach said:
2 were new, 3 others were not. If one more dies I will take back Cat. Would a Pictus Cat kill fish as big as they are? I have never heard they attack and kill fish as large as they are. Plus no marks on fish at all. If my plants are not giving off oxygen at night, and I have c02 going, why would I not run out of oxygen? There is no airstone going, and no surface agitation, so where would my tank get oxygen at night?
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I don't doubt that the CO2 may have something to do with it, but excess CO2 and lack of O2 are seperate issues. I really doubt there is a lack of oxygen in your water. Too much CO2 can be harmful to fish by poisoning them and/or causing ph fluctuations. Running an air stone at night will help to excess CO2 to gas off. People who run pressurized often use a timer to stop CO2 injection at night, but that wouldn't work with a DIY generator. It would be helpful to take a ph reading right before the lights go out, and another reading right before they come on.

I wouldn't discount the idea of the pictus being the culprit, either. Certainly a possibility.
 
thebach said:
2 were new, 3 others were not. If one more dies I will take back Cat. Would a Pictus Cat kill fish as big as they are? I have never heard they attack and kill fish as large as they are. Plus no marks on fish at all. If my plants are not giving off oxygen at night, and I have c02 going, why would I not run out of oxygen? There is no airstone going, and no surface agitation, so where would my tank get oxygen at night?
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Like I said before, in a tank as planted as yours enough oxygen would have built up throughout the day for all your fish. A heavily planted tank should provide just enough oxygen for 2 days (especially with enough CO2). It's also possible with the 2 new additions dieing off that they were sick and killed the other 3. Did you think about that? When you added them to the tank did you add the water from the bag?

All in all, pictus are not community fish. If they didn't kill those fish, then they will in the future. They're about as predatory as you can get in a catfish.
 
I completely agree with Aqualung and Cdawson here, and would add this is why I was driving so hard on the pH and KH question. Without knowing how many ppm of CO2 you have, there is absolutely no way to know if this is even the culprit. While O2 and CO2 are independent of eachother, it is still entirely possible to have an adequate level of 02 and still poison your fish with CO2.

Test both in the morning and at night to see how much CO2 you have. Again, if you are injecting too much CO2, it is entirely possible that an airstone is not going to create enough surface turbulence to make a difference. Further, if you are injecting too much and don't have adequate buffering, turning of the CO2 at night could cause such massive pH swings that it too would kill your fish.
 
Last night I set up a valve where I can let the c02 just go into the air and not the tank, then I turned c02 back on this morning. I also ran an airstone last night. I did not have any deaths last night, but I won't feel any better until it's been a week. So c02 is used by the plants during the day, but they don't use it at night so the c02 could poison fish? If thats the case then I have it fixed. If it's oxygen depletion at night I have that fixed too. Just a matter of waiting now. What is the best way to test c02 ppm?
 
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well, I've had airstone running at night for 3 days and c02 off at night. This morning I found another gourami dead. As usual, no marks, died at night, didn't act funny for a few days and die, just dead in morning. So I guess now I try taking my Pictus Cat back and hope he was the killer. If it's not him I am totally lost as to why I have fish dying at night only.
 
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