Can Co2 kill fish?

Diann62

AC Members
Mar 11, 2008
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Ontario, Canada
I've got a fairly heavily planted 110 gallon tank. I have 108 watts of light that I leave on for 12 hours/day. My substrate is flourite and I fertilizer twice a week with Big Al's all purpose plant food supplement. My plants initially looked phenominal and were growing like weeds. Then they started uprooting and not looking so hot. I checked the levels yesterday and the iron was 0 and CO2 was 4-6. The nitrate/nitrate/ammonia was all 0. I bought flourish iron and dosed the tank. I'm not thinking I want CO2. The guy at the LFS said it's really not necessary and you could kill your fish. I'm confused because I know a lot of people here use CO2. I've seen CO2 tablets and there's also a metal bar that somehow gives off CO2. I saw another system with hoses and tubings and I'm assuming you get a CO2 cylinder and somehow hook that up. Does anyone know if the bar works? What about the tabs? Also, has anyone had any fish die because of CO2? I'm confused at what to buy for CO2. Any help is much appreciated. Thanks.
 
You have a very low light tank, dosing CO2 would be unnecessary. What kind of plants do you have in there right now? They may not be suitable for your setup.
 
First, yes CO2 can kill fish, but it is so unlikely that I wouldn't worry about it.
The only way it would probably happen is if you had a ton of plants and I mean a ton of plants in your tank (almost no swimming room) with a ton of fish and you were injecting pressurized CO2 24/7 with no air stone running overnight.

That said, IMO pressurized CO2 is still the way to go although like BoredAgain says, in your setup it's almost unnecessary and your plant problems may be due to the keeping middle to high light plants in a low light setup.

Regardless, if you want to see if CO2 would benifit your setup I recommend getting yourself some Flourish Excel and dosing that for a month or so. If the plants perk up....then you may want to consider adding some other kind of CO2 source as Excel can be expensive when used on a tank the size of yours.
 
it takes quite a bit of CO2 to kill your fish. in any case a rampant pressurrized system may be capable...
but there are plenty who run CO2 24/7 and see no ill effects. I run it withtthe lights on . I use a solenoid which turns the CO2 line off when the lights off.
typically you will see the fish gasping for air if there is too much CO2 and not enough O2.

you may or may not see benefits to CO2(tho I personally believe it doesn't hurt to add it)
 
The only way it would probably happen is if you had a ton of plants in your tank and you were injecting pressurized CO2 24/7 with no air stone running overnight.

Haha. That is pretty much my setup. I've had a few close calls when adjusting my bubble counter. Thats actually how I set the rate. When I see them gasping I knock it down a bit. Do a water change. And add air stone for thirty minutes or so. They are good to go after. Ive only had it happen once or twice.

Yamato shrimps seem to turn blue when its too high as well and they'll jump out of the tank. lol.
 
Diann, I think it might you if the basics of plant growth were layed out.

Photosythesis is the process of which plants metabolise and grow. There are three basic components to plant growth requirements: Light, CO2, and nutrients (potasium, nitrates, trace elements, etc). Light drives how much of the nutrients and C02 is taken up by the plants.

In your case, you have low light 108 watts in a deep 110 gallon tank. Most stem plants will have a hard time growing in these conditions. However hardier plants such as anubias, java ferns, and mosses are much better suited for lower light conditions and can possibility do okay in your setup. These hardier plants won't require much nutrients or C02 because of the low light conditions. Adding CO2 definitely won't hurt, but it's not absolutely necessary.

To answer your question,

1) Yes excess CO2 can kill fish
2) The CO2 tablets you drop in your aquarium, and the metal bar gismo (carbo-plus) do not work.

-John N.
 
I wish I could up the wattage, but it's already bright enough and I'm planning on getting discus, and I know they don't like it so bright. It urks me that the guy from the LFS told me that 108 watts was enough for all the plants I bought. Newbies like me depend on their expertise. Is there something on this site that goes into more detail about plant growing?
 
theres planted tank forums. how many watts or lumens(still dont know if that applies in growing plants in water) doesnt always make the tank brighter... you cant really look at a light and determine how many watts it puts out by the brightness of it... i dont thnk
 
If you have a pressurized setup, with a decent diffusion method, it is much easier to kill fish with co2 than previous posters have described.

Whatever, I'm dumb, but I've had a few close calls and one big accident where I wiped out most of my tank with co2 since I went pressurized.

I inject co2 into the intake of my cannister filter, almost 100% diffusion. I accidently bumped the bubble rate up a little high(ok, so maybe it was like 100bps(basically so fast you could never count it) in 45g tank, sue me:omg:)


Point is, until you get used to your tanks needs by paying attention to both bubble count and drop checker, it's fairly easy to kill fish with co2.
 
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