# Can too much co2 kill fish



## duzzy

Hi there,

I have been loosing fish nearly every day for the past week. All my levels are great the only thing I can think of is too much co2. I have a heavily planted 130 litre tank I am running 2x2 litre DIY co2 bottles recipe is for each bottle 2 cups of sugar satchel of bakers yeast and water. Is this too much and can co2 kill fish via overdose.

To my way of thinking too much co2 means less o2 is this assumption correct?

Darren


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## davemonkey

Too much CO2 CAN kill fish. If this were the culprit, you should see the fish gasping for oxygen at the water surface or hovering at the flow outlet of the filter. If the fish are not doing this, I would not suspect CO2 (but I've been wrong before... :-# ) . 

CO2 supplementation will also lower your pH to some extent. Have you checked what your pH is?

-Dave


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## houseofcards

Is your water clear? Did some of the mix get into the tank. I doubt you would generate too much co2 with that.


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## stuckintexas

wow, a whole satchel of yeast. that might be cause for too quick of co2 production yielding higher concentrations and making your fish gasp at surface and eventually suffocate.

i use 1.5 cups sugar, 2 tsp baking soda, drinking water or spring water, and 1/2 - 3/4 tsp rapid rise yeast. the whole satchel for me is about 4 batches with this recipe.


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## JanS

The one thing with DIY C02 is that you can't really control what's going into the tank, so as stated, if your fish are gasping at the surface, there's probably too much.

You could try adding an air stone to see if that helps at all.


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## duzzy

Hi there are no fish gasping at the surface and yes the water is clear. I added 10 tetras would that cause the bio filter to crash?

Regards Darren


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## davemonkey

duzzy said:


> Hi there are no fish gasping at the surface and yes the water is clear. I added 10 tetras would that cause the bio filter to crash?
> 
> Regards Darren


I don't think that would be likely in a heavily planted tank (the plants take care of bio-load pretty well). Is it just the new tetras that are dying? Maybe a bad batch of fish or your water is VERY different from where they came?


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## ray-the-pilot

Here is a good, safe and easy way to add CO2 to your tank and estimate the correct level.

Buy a 1 liter seltzer siphon. They are available in many house ware stores and on line. Fill it with water, charge it and put it in the fridge. The charge is 8 grams of CO2. The charged bottle is 8,000ppm of CO2. 

Run your tank for two days with good aeration and no additional CO2. 

On the third day check the pH of your tank water. Then add to your tank 100 ml of the 8,000ppm CO2 solution for each 10 gal of tank water. (If you have a 50 gal tank add 500 ml of solution). Check the pH of your tank again. This is a safe level of CO2 for fish. 

In the future you can just check the pH of your tank periodically to see if the CO2 is under control.

BTW: For months I manually regulated my CO2 by adding this amount twice per day.

BTW2: Are your tetras neon tetras? They are subject to neon tetra disease and infected batches die off in the way you describe.


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