Has anyone had issues with low levels of CO2 killing off fish?

[PaigeIs]

I have a 20 gallon planted tank to which I recently added CO2.  I have one other tank also running CO2.  In this tank, I started CO2 a few days ago at 1 bubble per second.  The CO2 drop checker barely turns green, so I assumed I was in a safe zone, until my fish started to die. In two days I've lost three fish and a shrimp :(.   Several of the remaining fish are lethargic, hiding, slow to eat etc.  I've not witnessed any gasping at the service.  I've shut off the CO2 and did a 50% water change, but I don't know that the CO2 is the problem, it's just the only variable that has changed recently.  The dead fish did not show any visible signs of illness.  I want to run CO2 to improve plant growth/control algae but not at the expense of the fish.  Thoughts? Advice?

Parameters

• 1 sponge filter with airstone
• Tidal 35 HOB
• Temp: 74.5
• Ammonia: 0
• Nitrates: 20ppm
• Nitrites: 0
• KH: 10
• GH: 12
• PH: Before CO2  7.8  after CO2 7.6

Fish (as of today)

• Platy maybe 10, only 3 adults)
• Otocinclus 4 
• Amano Shrimp 1

Plants:

• Anubias: 4
• Buce: 5
• Crypts: 2
• Scarlette Temple: 4
• Dwarf Lily: 1
• Dwarf Sag: 2
• Water Wisteria:1
• Floaters covering about half the tank

 

 

[Fish Folk]

So sorry to hear. I've never had this problem. But I have experienced a related situation: CO2 can cut through buffer, and if you have soft water, can totally crash your pH. Now, your readings only indicate a slight drop off in pH, assuming that your test is correct. So these fish deaths may have been due to something else. But if you can isolate as many variables as possible, you might expand your search for a cause. If the CO2 install was the point from which you began to see fish die off, perhaps you could figure something out there. What might have impacted your fish health starting at that point? Obviously, CO2 is a possibility.  But might the hardware have been dipped in / washed in something toxic? Could the gas canister / source be suspect? Even someone helping who used a toxic hand lotion could be part of the story. Much as a 20 gal is a decent size, on the whole, it is still a very small volume of water. Was there a large water change that was performed in coincidence with the addition of the CO2? Just trying to brainstorm here . . . 

[PaigeIs]

@fishfolk   Thanks!   I've been trying to figure out the issue by looking at individual factors.  You've given me a few things to look at. I never even considered the CO2 canister or hand lotion.  I did a large water change when I found the fish and another small one today.  All but one of the fish are showing improvement.  Fingers crossed that the rest bounce back.  I am wondering if the issue was an ammonia spike.  Last week I was extra diligent when cleaning the gravel and notice a lot of bubbles coming up from the substrate.  Silver lining, now I have an excuse to get a bigger tank.  

[face]

is your co2 turning off at night? if you have automatic shutoff solenoids and timers can fail

[nabokovfan87]

On 7/16/2022 at 3:10 PM, PaigeIs said:

• 1 sponge filter with airstone
• Tidal 35 HOB

Keep an eye on the tidal for bypass. If you have any issues, please be sure to check the tidal thread or go ahead and send me a DM.
 

On 7/16/2022 at 3:10 PM, PaigeIs said:

Several of the remaining fish are lethargic, hiding, slow to eat etc.

This likely is oxygenation issue.  Cut the CO2 for a two days while we talk through and verify setup.  Can you take a photo of the amano shrimp and otos to show gill coloration and shell coloration please.

On 7/16/2022 at 9:13 PM, face said:

is your co2 turning off at night? if you have automatic shutoff solenoids and timers can fail

Very good question! One of the biggest things to check is the CO2 when it's under pressure, it might be something that changes from when you first set it up and you might be dumping CO2 into the tank unknowingly.  If you can, take a video of the bubble counter and show the diffuser in the tank so we can see how it's flowing.

Edited July 17, 2022 by nabokovfan87

[Fish Folk]

^Excellent recommendations^
 

Just as a basic aside… plants require light to respirate CO2. They use _oxygen_ after lights-off. Water can only hold a limited amount of dissolved gasses. Perhaps your issue is insufficient O2??

 

[Brandon p]

What are you running for CO2

[Mmiller2001]

Here's what too high of co2 looks like before they begin passing out. Once they pass out, there's still time to save them.

https://youtu.be/lPW8_WrigH8

[PaigeIs]

@nabokovfan87  Thanks!   I shut off the CO2 two days ago, when I found the first victim so I can't take a picture of the setup. The pressure on the tank is 50psi and the bubbles were flowing at 1 per second.  I checked it several times per day for the first few days of setup.  Also, I have a solenoid attached to a timer.  CO2 was going on one hour before lights on and shutting off an hour before lights off (a total of 6 hours).  The HOB is running normally: good flow, nothing running into the bypass.

As of today, all of the remaining fish seem to have bounced back.  Everyone's gills look to be a normal, no dark coloration.  The remaining shrimp molted yesterday and is hiding behind the heater.  

I will restart the CO2 tomorrow for a short period and post a pic of the setup. I also bought a Dennerle CO2 quick test so I can check the CO2 level in the water on demand.  I am still not positive that the CO2 was the issue, it just seemed like the most likely issue.  

On 7/17/2022 at 12:20 PM, Brandon p said:

What are you running for CO2

@Brandon p  I have a magtools regulator (cheapy) and a 2l bottle of CO2

Edited July 17, 2022 by PaigeIs

[nabokovfan87]

On 7/17/2022 at 4:18 PM, PaigeIs said:

The pressure on the tank is 50psi and the bubbles were flowing at 1 per second.  I checked it several times per day for the first few days of setup.  Also, I have a solenoid attached to a timer.  CO2 was going on one hour before lights on and shutting off an hour before lights off (a total of 6 hours).

I would suggest CO2 off 2 hours before lights out.  you're running a pretty short lighting window. Typical is ~8 hours or so I would believe.  When you check the CO2 itself, verify it 20 minutes after power on. Then verify it again 2-3 hours after it's been on to verify it isn't dumping in CO2. 

If you see the fish doing the same behavior after lights off or during any of the time when the CO2 is on, you need to turn the CO2 off and add aeration.