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Am I gassing my fish?

1288 Views 9 Replies 6 Participants Last post by  bill321
I am not new to keeping fish but I am new to keeping a planted tank.

I have a 33 gallon tank with pressurized Co2 that I did a Dry-Start for 8 weeks or so. Then I planted it and let it cycle for another 8 weeks. I am doing EI dosing with a 50% weekly Water Change. I had some initial algae issues but I cleared that up by reducing light, spot treating with Excel, and adding 12 Cherry Shrimp, 4 Ottos, and 12 Nerite snails.

I had some initial die off with the shrimp and Ottos, but I didn't think too much about that as the tank was still settling in.

But then 2 weeks ago I was at PetSmart getting something for the dog and saw they had Cardinal Tetras on sale for $1 each. I thought it was about time I put a nice school of fish in the tank so I bought the last 14 they had. They all seemed full grown so I took them home and gave them an acclimation period of about 1.5 hours where every 15 min or so I would put in about 1/4 cup of tank water in their bag. When I first added them to the tank I had the lights off and the only issue I had was the Tetras all stayed at the top gasping. I assumed it was because they came from the store right to my Co2 injected tank about an hour later they seemed fine and were swimming near the bottom and middle of the tank.

Everything seemed fine for the first few days but then I found some dead tetras one morning. I didn't think too much of it as I expected some loss. But then a few days later I found another dead Tetra.....And then another. And this morning I found another dead one stuck to my Korilla Nano and now just a few minutes ago I found another. I am down to 6 live Cardinal Tetras, 2 ottos, 6 Shrimp.....all the Nerite snails and hitch-hiker pond snails are still going strong (go figure).

The water parameters should be fine for these fish best I can tell. Ammonia=0 Nitrites=0 Nitrates=30~40ppm PH=6 to 6.4 (depending on how long Co2 has been on) KH=2 GH=4 Temp=26C

The only thing I can think of is that either these fish were all old when I bought them (maybe that is why they were on sale for a buck a piece) or I am gassing them to death with the Co2. I have a drop checker and I use some pre-mixed 30ppm solution from SuMo and my 4dkh drop checker stays green all the time, even after Co2 being off all night with an air stone on. I assume the solution is good because it is dark blue until it has been in the water for about an hour.

Anybody have any suggestions as to what I should be looking for?

I don't want to spend money on more fish until I get this straightened out. It is frustrating because my low-tech (heck it is no-tech) cheepy 10 gallon Betta tank is doing fine with 1 Betta, 4 White cloud minnows, and 1 Otto. All it has is the stock light/top, a 15 watt heater and a Whisper 20 filter. I spent hardly any money on that tank and it seems fine.....while my high-dollar high-tech show-piece tank seems to be a death sentence for my fauna !! :)

Thanks !


Here is pic from a few days ago. I think the Nerite snails are having an orgy in the bottom right corner. :)
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That is really a beautiful tank! I would be delighted to have one like that.

I doubt that the CO2 is the problem with the cardinal tetras. My guess is that they were not healthy when you first got them, not uncommon with that fish. If you had too much CO2 the tetras would be clustered at the top, "gulping air", probably at the right front corner, where the CO2 concentration is probably the lowest. I found that tetras and similar size fish do that pretty consistently when the CO2 level is a bit too high.
The Petsmart cardinals while cheap when on sale are notorious for die offs or contracting diseases. They can be a good deal but really should be quarantined. It looks like they may be the only fish in your tank at this point so just watch them for any signs of disease, treat if necessary, and don't introduce any new stock for a month until they are out of quarantine. Most of them should make it.

Agree that the tank looks awesome!
Well since the local PetSmart just got a new shipment of fish......I picked up 10 more Cardinal Tetras and 3 more Ottos last night. They are new fish as I bought all they had last week.

Gave them all a nice lengthy acclimation period with the lights off. The Tetras and 2 of the Ottos went in my Co2 tank and 1 Otto went into my crappy low-tech 10 gallon Betta tank.

This morning 1 Tetra and both Ottos were dead in the Co2 tank and the 1 Otto in the low tech tank is happily cleaning the glass and rocks !!!

This weekend I am going to make a trip into Denver to a "real" LFS and see if I have any better luck. I want to believe this is just the quality of fish from Petsmart not my tank. But so far it seems I have a choice.....a Co2 planted tank with healthy growing plants and dead fish......or a sparsely planted tank with Excel and live happy fish :icon_evil

But so far it seems I have a choice.....a Co2 planted tank with healthy growing plants and dead fish......or a sparsely planted tank with Excel and live happy fish :icon_evil

Lots of people have CO2 planted tanks without constant fish deaths... there is no need to narrow your choices like that unless you have given up already.

I agree with Hoppy that the problem has probably been the quality of the fish from PetSmart not your CO2 though it does look from the photo of your tank like you have little to no surface agitation. That is also why your drop checker is still green in the morning. Surface agitation from a spray bar or powerhead will facilitate O2 exchange into the water way better than an airstone. If you are injecting CO2 you should always make sure there is enough O2 in the water for the fish 24/7. The CO2 can be turned up if you have to compensate for any gassing out, there is no reason you can't have good CO2 and O2 levels simultaneously.

CO2 is the hardest thing to get right and unfortunately the learning curve sometimes includes algae and dead fish. You need to be able to learn from your mistakes.

FWIW... cardinals and otos are two of the fish that people have the most die offs from even if they don't buy them at PetSmart. They are both fish that are very sensitive to water quality and seem to get stressed easily too.

Regardless of where you buy them they may take up to a month to settle in before they are not prone to contracting disease or dying off. We are fortunate here in the Bay Area to have a couple of LFS that actually quarantine their stock before they will sell it. Really cuts down the amount of problems if you can find and purchase fish that have been quarantined.
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I'd say PetSmart.. I did the 1 dollar deal a while ago and bought 50 tetras and every one of them died... A week later I got 25 from user RMC here on the SnS, that was 6 months ago and every single one is still alive.

They are just too sensitive especially while on sale they get hustled around too quick and they cant survive that.
I think you guys were correct all along !

I think you all were right and it was the fish from PetSmart and not my tank or Co2.

This weekend I went to a "true" fish store where they quarantine new stock. They also mark on the tank the date they arrived and if they have been treated with anything etc.

I bought 12 Rasboras and 2 Celestial Pearl Danios and ....knock on wood.....3 days later all the fish are still alive and seem to be doing very well. By this time with the PetSmart tetras I would be down to a couple of fish ! :)

So I learned my lesson and will only buy from a true LFS or from other forum members from now on.

I know this isn't the best picture but it is hard to catch these little guys. They are only like 3/8 of an inch right now and are not shy at all. In fact they are chasing around the 2 remaining Cardinal Tetras I have and those tetras are twice the size of the CPDs. I just hope at least one of these is a male. I am not sure if they are both females or if they are just too young to be really colorful yet.


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Wow thats a beautiful tank. The big chain stores almost alway have inferior quality fish not worth the risk. 4 and still no deaths 4 and still no deaths.
So I am like 99% positive now it was just the "quality" of the Big Chain Store fish.

Oh and thanks everybody for the nice compliments !

I am just working on learning how to grow plants right now....maybe someday I will concentrate more on the scaping part. In fact I am already bored with what I have and have been thinking about ways to improve it. I can already tell this plant part of the hobby is way more addictive than just regular fish keeping :)

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