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Old 03-25-2007, 10:24 AM   #11 (permalink)
 
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Default Re: Just wiped out a tank of fish

Wrong again furballi.

It's not the pH drop that kills the fish. It's the high levels of CO2. The pH drops because because of the CO2.

And kH has nothing to do with it. It takes 30 ppm of CO2 to drop the pH of the water 1 no matter what the kH. That assumes of course that you are starting with a tank with no CO2 injection. But that first degree of drop takes ~30 ppm of CO2.

What part of "Low pH is the symptom and not the problem." did you not understand?

I will say it again and type it slowly so you can understand. pH changes caused by CO2 have no effect on fish. Of course if you get so much CO2 into the water that their gills can no longer function then you will harm the fish. But it's NOT the pH that causes that problem.

I have covered the reasons why pH changes due to CO2 do not harm fish in my FAQ. www.theplantedtankfaq.com

Also Tom Barr has shown that pH changes due to CO2 do no harm to fish.

Using CO2 to lower pH is an artificial means to do so. It does not change the hardness or TDS of the water. Normally when you lower pH you are also required to change the hardness and TDS. If this change occurs quickly you can cause problems with the osmotic balance of the fish. When CO2 is used to lower pH there is no change in the hardness or pH.

Again.... and I know it's hard, but you have to separate the pH and the CO2 levels. High CO2 levels will cause low pH. But the low pH is the symptom, not the problem.
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Old 03-25-2007, 10:25 AM   #12 (permalink)
 
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Default Re: Just wiped out a tank of fish

Quote:
Originally Posted by Ulan View Post
I'd assume that too much CO2 will build up a layer of CO2 on top of the water (CO2 is heavier than air), especially in those cases where you have a lid or a significant rim above the water line. This will invert the partial pressures of O2 and CO2 dramatically and lead to a situation where you will actually have more dissolved CO2 in the water than O2. And your poor anabantoid will also gulp down CO2 when he tries to get some oxygen from above the water surface.
This is very true. And it can and does happen. One of the reasons I like to keep my tanks full and run open top tanks.
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Old 03-25-2007, 05:46 PM   #13 (permalink)
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Default Re: Just wiped out a tank of fish

The pessurized CO2 system is a new addition to a well established tank, one that has comfortably weathered power outages in the past. I agree that lack of 02 killed the fish as opposed to overdose of CO2 but excess CO2 could deminish the carrying capacity of gases in the tank causing the depleted O2 levels.
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Old 03-25-2007, 08:22 PM   #14 (permalink)
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Default Re: Just wiped out a tank of fish

Quote:
Originally Posted by Ulan View Post
I'd assume that too much CO2 will build up a layer of CO2 on top of the water (CO2 is heavier than air), especially in those cases where you have a lid or a significant rim above the water line. This will invert the partial pressures of O2 and CO2 dramatically and lead to a situation where you will actually have more dissolved CO2 in the water than O2. And your poor anabantoid will also gulp down CO2 when he tries to get some oxygen from above the water surface.
Unless there exist an air tight top cover to build up the atmospheric pressure above the nominal 14.7 psi, we're not going to experience any abnormal CO2 build-up due to the molecular weight of CO2!
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Old 03-25-2007, 08:25 PM   #15 (permalink)
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Default Re: Just wiped out a tank of fish

The best thing to prevent this in the future is a power fail (normally closed) solenoid. You can also minimize the threat of this occurring with altering your CO2 setup.

Sometimes the CO2 injection rate is dependent on the back pressure of the water pump. I notice that my bubble rate increases 2-3x when my filter turns off. I have an external reactor connected to the output of my ehiem. In my setup, this would only fill up the reactor and not discharge into the tank until my 18" reactor fills. This would take several hours. I would get a CO2 burst when the power finally does turn on and my reactor then sounds like a waterfall. I have a bleed valve on my reactor for such occasions to drain the excess CO2.
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Old 03-25-2007, 09:06 PM   #16 (permalink)
 
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Default Re: Just wiped out a tank of fish

Quote:
Originally Posted by furballi View Post
Unless there exist an air tight top cover to build up the atmospheric pressure above the nominal 14.7 psi, we're not going to experience any abnormal CO2 build-up due to the molecular weight of CO2!
No, a simple rim is sufficient, a completely closed lid is not necessary. You can pour gaseous CO2 with a beaker. You can even kill a rat with CO2 in a container that is open at the top. Keep in mind that most planted tanks keep surface movement low and avoid airstones.

The easiest way to see this is with dry ice and hot water, because there you can observe the interface between the CO2 and the air.

Last edited by Ulan; 03-25-2007 at 09:15 PM..
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Old 03-25-2007, 09:45 PM   #17 (permalink)
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Default Re: Just wiped out a tank of fish

Quote:
I will say it again and type it slowly so you can understand.
LOL. Listen to REX he knows his stuff.
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Old 03-25-2007, 10:09 PM   #18 (permalink)
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Default Re: Just wiped out a tank of fish

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Originally Posted by Rex Grigg View Post
Wrong again furballi.

It's not the pH drop that kills the fish. It's the high levels of CO2. The pH drops because because of the CO2.

And kH has nothing to do with it. It takes 30 ppm of CO2 to drop the pH of the water 1 no matter what the kH. That assumes of course that you are starting with a tank with no CO2 injection. But that first degree of drop takes ~30 ppm of CO2.

What part of "Low pH is the symptom and not the problem." did you not understand?

I will say it again and type it slowly so you can understand. pH changes caused by CO2 have no effect on fish. Of course if you get so much CO2 into the water that their gills can no longer function then you will harm the fish. But it's NOT the pH that causes that problem.

I have covered the reasons why pH changes due to CO2 do not harm fish in my FAQ. www.theplantedtankfaq.com

Also Tom Barr has shown that pH changes due to CO2 do no harm to fish.

Using CO2 to lower pH is an artificial means to do so. It does not change the hardness or TDS of the water. Normally when you lower pH you are also required to change the hardness and TDS. If this change occurs quickly you can cause problems with the osmotic balance of the fish. When CO2 is used to lower pH there is no change in the hardness or pH.

Again.... and I know it's hard, but you have to separate the pH and the CO2 levels. High CO2 levels will cause low pH. But the low pH is the symptom, not the problem.

Hmmm...it requires a very high level of CO2 in the water column to block the uptake of oxygen. High CO2 levels may cause some inhibition of respiration in fish, but it will take an abnormally high level of CO2 in the water to impede diffusion from the gills. Of course the ability to tolerate high level of CO2 will vary from species and condition of the fish.

I was tinkering with CO2 injection many years ago and accidentally lowered the tank's pH from 8.2 to 6.6 over several hours. Since the local water has a KH of about 10, the amount of dissolved CO2 must be at least 80 ppm. There was no loss of inhabitants (neons/SAE/otos) in that tank. Also note that it is very difficult to raise the concentration of CO2 above 60 ppm (room temperature) unless there is a malfunction of the regulator/needle valve assembly.

You are naive if you believe that a very sharp change in temperature, pH, KH, etc do not kill fish.
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Old 03-25-2007, 10:16 PM   #19 (permalink)
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Default Re: Just wiped out a tank of fish

Quote:
Originally Posted by Ulan View Post
No, a simple rim is sufficient, a completely closed lid is not necessary. You can pour gaseous CO2 with a beaker. You can even kill a rat with CO2 in a container that is open at the top. Keep in mind that most planted tanks keep surface movement low and avoid airstones.

The easiest way to see this is with dry ice and hot water, because there you can observe the interface between the CO2 and the air.

Building a layer of CO2 at the surface of the tank with a flow rate of several 3 mm bubbles per seconds? That's quite an imagination.
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Old 03-26-2007, 04:01 AM   #20 (permalink)
 
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Default Re: Just wiped out a tank of fish

Well, as expected this thread turned out to be an exciting one. So far, its been spirited, but not abusive. I applaud the combatants.

Nobody is challenging that rapid changes in any number of parameters isn't bad for fish. The point is that very high levels of CO2 kill fish, not the low pH that is a consequence of high CO2. Independent versus dependent variables.

In the absence of a drop checker, we really don't know what our CO2 levels are. My KH is now about 3.4 (LaMotte test kit) and I have my calibrated pinpoint controller at 6.0 to 6.2. This yields a "CO2 concentration" of 102 to 64 ppm and the fish are fine. When the solenoid sticks and the pH drops to 5.5, a "CO2 concentration" of 320 ppm, the fish come to the surface. When the concentration drops to about 150 ppm as indicated by a pH of 5.8 everything is hunky dory.

Why do the fish gasp for air at the surface when the solenoid sticks open and then resume their normal fishy routines at mid and lower levels once CO2 levels drop?

By the way, its a great way to take inventory if you've lost track of what fish you have....
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