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Old 09-22-2008, 04:23 AM   #31 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

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Originally Posted by hoppycalif View Post
In a fish only tank there is no CO2 injection to make the pH change. In fact the pH should remain virtually constant unless something generated in the tank makes it change.
What do you think fish do? They inject CO2 into the system.

If you are saying that CO2 is removed from your tank by aeration, this is true. But the rate is very slow compared with the rate consumed by plants (at least in my aquarium).

Here is the point. You can make up any story you like, but have you used a pH controller? I have. Now it may go on at night without me knowing about it but whenever I've looked it was not working and the pH was constant.

During the day it is basically on all the time.
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Old 09-22-2008, 05:55 AM   #32 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

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Originally Posted by chagovatoloco View Post

"Fish keeping does not add CO2 to control pH though.
They use buffers like baking soda.

When the pH drops fast, it's a sign of some cycling going very wrong in a fish only tank, when you add say 4 Kh more baking soda to a 2 Kh tank, the fish will die and the pH will shoot up fast.

CO2 is not the same.

Think about this thought question:

What happens if I do a massive 60-70% weekly water change when I add CO2 and have a pH of 6.2, and the incoming tap is 7.6?

How much pH change do I see over a few minutes?
About 1 full unit.

The KH is the same with respect to the tap water and the tank water.
So the osmotic difference is the same, CO2 is not a salt.

Now, think about what folks do using CO2 and in planted tanks with 50% weekly water changes......

Any reports of dead fish?
None.
Healthy happy fish and plants?
Yes.

I'll let you ponder the rest and see how pH, at least in and of itself is not really the issue, rather the KH/buffering systems that change rapidly, and thereby also by definition, change the pH, are the real issue with respect to fish health.

Fish hobbyist hardly know beans about GH, KH, and chemistry of the pH/KH/CO2 system as it is. And then only in relation to ambient, not fertilization with CO2 ppms.

So that causes myths and confusion."
Partially deleted to save band width.

Let me point something out. I consider myself at the intermediate level when it comes to growing plants in an aquarium but I am a professional (which means that I get paid to do this) expert at chemistry and my special interest right now is water chemistry.

So I probably know more than Tom Barr and Takashi Amano combined about that subject.

So if Tom Barr says:

“Fish keeping does not add CO2 to control pH though.
They use buffers like baking soda.”

He obviously doesn’t know anything about water chemistry.

I don’t know how to put a full semester of P. Chem. into a short post but let see if I can explain something.

CO2 = H2CO3= HCO3- = CO3(-2)
What this means is that any of these species will convert to the other and all are present in water. The amount of each depends on the pH and the amount of spectator ions like Na (referred to in aquarium literature as kH).

So when you add baking soda (NaHCO3) to your tank you are adding CO2 as well. In fact, one of the ways they make baking soda is by adding CO2 to a solution of Na2CO3.

Plants can crack out most of this CO2 and do so until the pH reaches about 8.4, which is the equilibrium point for the HCO3- = CO3(-2) reaction.

So when you add CO2 you are simply adjusting the relative levels of H2CO3, HCO3- and CO3(-2).



When Barr says:
“When the pH drops fast, it's a sign of some cycling going very wrong in a fish only tank, when you add say 4 Kh more baking soda to a 2 Kh tank, the fish will die and the pH will shoot up fast.”

(Let me point out that he is a little confused about whether the pH goes up or down but that is not my point).

My point is that when you add 4kH more baking soda, the pH will go to 8.4 and you will increase the CO2 by 70 ppm (This CO2 is not usable by plants; since, they cannot crack it out at that pH). You could get every mg of this CO2 out simply by adjusting the pH down.

Now this is my experience after keeping fish over 30 years.

In a low kH/gH tank changes in pH are not necessarily fatal; however, lower pH is beneficial/necessary for many species. If you want to keep and breed these you will have to maintain a low pH.


BTW: There is no place in the Barr quote where he says he actually used one only the same type of off the top of your head stuff that everyone else is using on this thread. So far, no one has actually used one; so, they are all hypothecating.

Last edited by ray-the-pilot; 09-22-2008 at 06:01 AM..
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Old 09-22-2008, 06:16 AM   #33 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

Quote:
Originally Posted by ray-the-pilot View Post
CO2 = H2CO3= HCO3- = CO3(-2)
What this means is that any of these species will convert to the other and all are present in water. The amount of each depends on the pH and the amount of spectator ions like Na (referred to in aquarium literature as kH).

So when you add baking soda (NaHCO3) to your tank you are adding CO2 as well. In fact, one of the ways they make baking soda is by adding CO2 to a solution of Na2CO3.

Plants can crack out most of this CO2 and do so until the pH reaches about 8.4, which is the equilibrium point for the HCO3- = CO3(-2) reaction.

So when you add CO2 you are simply adjusting the relative levels of H2CO3, HCO3- and CO3(-2).
Ray, Since you have knowledge of organic chemistry, I'm wondering if you could answer something for me. Allow me to get off topic for just ONE question, PLEASE!?!?!?!.

Is this similar to what happens when sugar is added to a planted tank? Could it actually make CO2? (Not that I would condone this or practice it...just curious about something I read. )

Thanks,
Dave
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Old 09-22-2008, 07:02 AM   #34 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

Boy I feel badly for the poor guy who started this thread and simply wanted opinions on a co2 system. He's probably taken up a different hobby by now, scared to death of the crazy people in this one.

Anyway the bottom line is there is more than one way to do things. I never said a ph controller doesn't work I stated and it is a "fact" that it isn't needed to have a successful planted tank. So for a newbie it's probably easier to keep it simple. If you like your PH controller that's great and you should continue to use it.
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Old 09-22-2008, 07:02 AM   #35 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

No, this is not the same thing. H2CO2, HCO3 and CO3 are basically the same thing with different amounts of H+ stuck to them.
Sugar is completely different. It is C6H12O6 and doesn’t react anything like the carbonate system.

The question whether sugar will turn into CO2 in your tank is actually an interesting question!

I can say with some assurance that sugar will be converted to CO2, if you have aerobic conditions in your tank.

All organic compounds are eventually converted to CO2 and water. The problem is that it is not like simple burning. In a biological matrix the sugar will be oxidized into a lot of intermediate compounds before it finally goes to CO2 and water. What these are and how they affect your fish/plants is hard to say.

My feeling is (which means this is an educated guess) that adding sugar to your water will promote the growth of a lot of bacteria and your tank will get cloudy and O2 levels will drop.

This guess is based on what happens to my wife’s humming bird feeder when she doesn’t sterilize it correctly.
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Old 09-22-2008, 07:06 AM   #36 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

This could become an informative and interesting thread, even though we are poaching on the originator's thread, but injecting insults prevents it from being that. Perhaps someone wants to start a separate thread to discuss the subject.
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Old 09-22-2008, 07:07 AM   #37 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

Your probably right.

I'll just pass on future post since I seem to be the one trying to swim up stream.

BTW I agree that it is not necessary to have a planted aquarium.

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Old 09-22-2008, 10:25 PM   #38 (permalink)
 
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Default Re: CO2 system suggestions for a 75gl tank

This has been a very informing thread. I just got a ph controlled co2 system. I love it. I use a drop checker with 4dkh solution to monitor co2. I really don't care what the ph is set too. This is a discus tank so i don't mind a low ph, but my water parameters are 6.08PH, 5GH and 4kH.

Earlier in this thread it was stated that phosphates can alter the reading of a ph monitor probe. It was also stated that it can effect the drop checker results. Can someone go into more detail on this? What levels of phosphate have dramatic effects on the ph controller's reading? If using a 4dkH solution in your drop checker, does phosphate have any impact?

This is a great thread for anyone with questions about co2... lots of unasked questions answered here!

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Old 09-23-2008, 09:14 AM   #39 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

The reason for using a drop checker is to isolate the water used to determine the ppm of CO2 from anything in the tank water, other than the CO2. The tiny amount of water in the drop checker has to be free of the ions that would affect the pH or KH, except for carbonates, which bring that water to a 4 dKH hardness (alkalinity).

I have never found a way to determine how "contaminated" the tank water is, and how it will affect the pH or KH. It must be possible to do that, if you have the test equipment needed. I do know that every person I have heard from, either by comments in forums or in person, who measures their CO2 concentration by using the pH/KH/CO2 table always gets a number that is too high, never too low. Typically I hear that someone keeps his tank at 120 ppm of CO2 and the fish are happy as a lark. That just isn't possible. I know from my experience that a ppm of CO2, based on a drop checker, that makes the checker really yellow will kill even guppies, and that would be somewhere in the neighborhood of 100 ppm of CO2. It isn't known, to my knowledge, how much concentration of CO2 kills which fish, but that number is almost certainly less than 100 ppm. The most recent information I have is from Tom Barr, using a precision CO2 concentration meter, who found that concentrations around 40-50+ ppm don't bother very small fish, but they do bother large fish. I think this is why so many of us have found that keeping our drop checker in the yellow-green area doesn't bother our small fish.
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Old 09-23-2008, 10:49 AM   #40 (permalink)
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Default Re: CO2 system suggestions for a 75gl tank

Quote:
Originally Posted by StevieD View Post
This has been a very informing thread. I just got a ph controlled co2 system. I love it. I use a drop checker with 4dkh solution to monitor co2. I really don't care what the ph is set too. This is a discus tank so i don't mind a low ph, but my water parameters are 6.08PH, 5GH and 4kH.

Earlier in this thread it was stated that phosphates can alter the reading of a ph monitor probe. It was also stated that it can effect the drop checker results. Can someone go into more detail on this? What levels of phosphate have dramatic effects on the ph controller's reading? If using a 4dkH solution in your drop checker, does phosphate have any impact?

This is a great thread for anyone with questions about co2... lots of unasked questions answered here!

Stevie D
Phosphates in your water do not affect the reading of your pH meter. The pH it gives you is correct for any buffer system. The issue is how the pH of your tank corresponds with the level of CO2 in your tank.

The whole thing comes from tables like this one:
http://www.aquatic-plants.org/articl...es/04_co2.html

If you go to this table, you will see that for your tank parameters at a pH of 6.08 you are well into the danger zone of CO2 level and it would seem that your fish are going to die. In fact this doesn’t happen because you have some other buffer system working in your tank (probably PO4). These other buffers interfere with the theoretical pH / kH / CO2 curve and give inaccurate readings.

When you use a bubble counter you fill it with a known 4.0 kH solution with no impurities. One part of the counter is in contact with the tank water and CO2 diffuses from the tank water and dissolves in the 4.0 kH solution. Because of the chemistry, after a while, the level of CO2 in the checker is the same as in your tank. Because there is no extra buffers in the drop checker, you can measure the CO2 using the pH of this solution. Typically this is done with a pH indicating dye. The color of the dye gives an indication of the pH and by inference the level of CO2.

Generally speaking what is in your tank water should not affect the drop checker unless some tank water contaminates the special solution in the drop checker.
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