Fish dying for no apparent reason, what gives?

[Watcher74]

Well, one reason why it didn't happen at first would be that the plants are thriving more and more as the time goes by.

So during the day they are using more CO2 than before, but at night they are using more Oxygen than before.

So eventually the fish would start to die, gradually at first, and then more and more fatalities the farther it goes without some change.

 

[thebach]

I trimmed back my Hornwort some, it was really growing. So should I turn c02 off at night and run airstone or leave it on and run airstone? Or turn off c02 and not run air stone?

 

[benedictj]

Woo...TYPO, that is really misleading. Gouramis and the like have the ability to take air directly, but that does not mean that overdosing CO2 wouldn't kill them. They do primarily breathe through gills.

Incidentally, how much RO water are you using? If you are using 100%, then you certainly have next to no KH. Also, how big is the tank? What measurements are you using for your yeast? (The trad 2 litre setup is designed around the requirements of a 30 gallon).

 

[thebach]

I have a 2 liter DIY c02, 2 cups of sugar and 1 teaspoon yeast. My tank is 20 gallon. I have a valve that I can install to turn down the c02 level. As far as RO water I use half RO and Half tap. It must have something to do with oxygen levels, it didn't start happening until plants really started to grow and fish are dying at night. So I'm wondering if I just need to run air stone at night and leave c02 alone, or turn down or off c02 at night.

 

[racingjason]

How are you turning down the CO2? And I think 2 liters is too big for a 20g, I had a 1/2 liter on a 15 and it made enough to get the CO2 up to 50ppm.

 

[cdawson]

I have 2 real nice Clown Loaches, small red tailed shark, 4 tiger barbs, 2 gouramis, and a small pictus cat. There is a 1 tetra, need to get a few more. Would it be better to turn off c02 at night or run airstone at night and leave c02 on?

What fish are you finding dead? Pictus cats are highly predatory and will quickly kill off anything half it's size. I don't recommend getting any more tetras as by the time you read this the last one will probably have been eaten already. My guess is that either you're getting a CO2 overdose at night (which is unlikely due to the amount of plants you have), or your pictus is killing your fish off one by one. Which is more likely than the CO2 overdose, especially seeing as a DIY unit is perfect for anything under 30 gallons. You have far too many plants for it to be the CO2 killing off your plants unless you're using well over a bubble every 3 seconds.

 

[thebach]

If it was my cat, why are fishing dying only at night and why do the dead fish have no marks? Also, why did it just start to happen? The dead fish have all been as large as the cat, and I have never seen him bother anyone. It started to happen just when my plants were really getting heavy. An oxygen drop at night makes a lot of sense, the cat killing fish at night maybe, but the evidence seems to say fish are suffocating at night. Maybe tomorrow I will take cat to fish store, but still leaning toward oxygen drop at night now that I've been reading about it.

 

[knashash]

just run the air stone at night and leave the C02 going

 

[cdawson]

If it was my cat, why are fishing dying only at night and why do the dead fish have no marks? Also, why did it just start to happen? The dead fish have all been as large as the cat, and I have never seen him bother anyone. It started to happen just when my plants were really getting heavy. An oxygen drop at night makes a lot of sense, the cat killing fish at night maybe, but the evidence seems to say fish are suffocating at night. Maybe tomorrow I will take cat to fish store, but still leaning toward oxygen drop at night now that I've been reading about it.

Pictus cats hunt at night, and and like I said before there's no possible way that a tank likes yours being as heavily planted as it is would not run out of oxygen during the night. Were any of the fish that died new?

 

[thebach]

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?