Is there a danger in...

Guppypuppy

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May 5, 2008
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Is there a danger, for plants or fish, by maintaining an inconsistent CO2 level to your tank?

My pH runs about 8.2 if I were to add CO2 am I correct in that providing CO2 may bring the pH down?

Our water is very hard. Calcium builds up on anything in the tank in just a day or two. While I know this is hard on the equipment are there any benefits to having such hard water?

I am just full of questions. Thank you for your time.
 

rusticitas

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(I think I understand this properly, my friend a Chemistry professor has quite patiently explained this to me on many occasions.)

Adding CO2 will react with bicarbonates in the water, forming carbonic acid, which does in fact lower pH. I do not think we add enough CO2 to do any danger to plants and fish in the tank, if done properly. (That is, adding enough to be non-limiting, not dumping in a tremendous amount.) Also, how one goes about getting the CO2 to dissolve into the water as well.

My city's water sounds opposite of yours. It is virtually like RO water, with a neutral pH. I add "GH Booster"/Equilibrium and use CO2. By using a drop checker with 4dKH reference my pH doesn't really go below 6.5-6.7 (I have not done any scientific measurements, or at least not consistently).

Fish and plants seem pretty happy, no deaths.

Now, last year when I went away for a long weekend, I had somehow opened up the needle valve on the CO2 effectively upping the dose 4-5x! When I came back the plants seemed ok, but there were rotting fish carcasses all over the tank... *Except* for the Goo-Obo gudgeons! Tough little mo-fo's.

-Jason
 

tedr108

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It will be virtually impossible to avoid algae with inconsistent CO2. Algae is not dangerous to your fish. Algae can, however, take over your plants by attaching to them. The only cure for that in most cases is to prune off the affected leaves.

Yes, CO2 lowers your pH -- with such hard water, however, your pH will be more stable and not lower as much as in a location with soft water.

Water can be too hard for some fish and plants. You might have to choose your critters and plants accordingly.
 

Carissa

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Jun 8, 2007
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Adding x ppm of co2 will lower the pH by x amount no matter what the hardness of your water is to start with. A tank with sufficient injected co2 will be about 1.0 pH lower than if the tank had no injected co2. So if you are starting with 8.0 pH, after you inject co2 you will be down to 7.0. If you start at 7.0, you will go down to 6.0. Hardness does not change this calculation.

However, this type of pH change is not the same as changing pH via other methods. It can fluctuate quite a bit if co2 fluctuates and the fish seem unaffected. Fish that like lower pH usually also like softer water, and adding co2 does not change your hardness, therefore it doesn't change the type of fish that will do well in your water...if you have hard water, choose fish that like hard water/higher pH. Co2 won't matter.

However as has been mentioned, fluctuating co2 is a terrible thing for plants. It's better to have no co2 injection than to have it fluctuating. Reason being that plants adapt to higher co2 levels when exposed to it. When suddenly co2 drops, the plants cannot adapt quickly, and therefore cannot get enough carbon anymore. This leads to a whole host of problems related to the carbon deficiency your plants will then experience (since carbon is the major thing that plants are made of....if they can't get enough, they can't grow or repair themselves), including algae, leaf loss, holes in leaves, and sometimes just total die off especially with faster growing plants.

In general, hard water is better for plants than soft water, as it contains more of the things plants need (such as magnesium, calcium, iron, etc.). Some plants are an exception to this though so research your plants before you get them.
 

aquabillpers

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Carissa;25224 said:
Adding x ppm of co2 will lower the pH by x amount no matter what the hardness of your water is to start with. A tank with sufficient injected co2 will be about 1.0 pH lower than if the tank had no injected co2. So if you are starting with 8.0 pH, after you inject co2 you will be down to 7.0. If you start at 7.0, you will go down to 6.0. Hardness does not change this calculation.

Is there a limit to how much CO2 can lower the pH in water that has very high KH?

Assume water with a very high KH that produces a pH of 9+ without CO2 injection. Would injecting CO2 move that pH at all? Would it lower the pH below 8.0?

Bill
 

Guppypuppy

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May 5, 2008
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Thank you all for your insight. I think I am starting to get a handle on how all these factors are related to each other.

What amazes me is that for each X ppm of CO2 the pH would be lowered by a corresponding amount. I am correct thinking that at a pH of 8.2 there are 10X fewer H+ atoms than there would be at pH 7.2? What is going on with the H+ or OH- atoms as CO2 goes up?

Thank you.
 

VaughnH

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If the KH is 9, and you have no injected CO2, the ppm of CO2 in the tank will be around 3 ppm, or near that. So, the pH will be about 8. If you now add about 30 ppm of CO2 the pH will drop by 1.0, and will be about 7. In order to have a KH of 9, you have to be able to dissolve about 160 ppm of carbonate in the water, so the limit is the solubility of the carbonate compound involved. But, bicarbonates are very, very soluble in water, so that will give just about any KH you want. And, as the pH drops with addition of CO2, carbonate compounds become more soluble too.

I think what this says is that in the range of concentrations of CO3 or HCO3 and CO2 that we are interested in, there is nothing in to prevent the pH and KH from assuming whatever values are needed.
 

Carissa

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Jun 8, 2007
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This is the formula:

CO2 (in PPM) = 3 * KH * 10( 7-pH )

This is only accurate assuming that you have nothing in the water to change pH other than carbonates, which is why it doesn't work reliably in most practical situations since pH can be skewed by many things other than carbonates.

Injecting co2 reacts with water in this way:

H2O + CO2 = H2CO3 (carbonic acid) a weak acid

KH = HCO3 (bicarbonate) a weak base

Carbonic acid and bicarbonate do not react with each other....the bicarbonate works as a buffer by reacting with strong acids and creating a weaker acid so the pH doesn't drop as much....for example -

HCl (hydrochloric acid) + HCO3 = Cl- + H2CO3

Therefore water with enough carbonates in it will be able to handle a larger amount of additions of strong acids without causing the pH to drop as much as it would otherwise (hence the 'buffer'). But adding the weaker carbonic acid by injecting co2 does not react with the bicarbonates, and therefore the amount of bicarbonates in the water prior to adding co2 has no effect on the drop in pH due to adding co2, as they simply don't react with each other.

If any of this is inaccurate someone correct me....I'm not a chemistry expert by any means. :)
 

Guppypuppy

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May 5, 2008
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That really helped me to figure out what is going on the only thing I found different was:

Carissa;25247 said:
H2O + CO2 = H2CO3 (carbonic acid) a weak acid

CO2 + H2O → H2CO3 → H+ + HCO3−

Thank you! That H+ atom then drives the pH level up. I knew it had to come from somewhere I just wasn't sure where. Thanks again.