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Old 03-26-2007, 04:42 AM   #21 (permalink)
 
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Default Re: Just wiped out a tank of fish

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You are naive if you believe that a very sharp change in temperature, pH, KH, etc do not kill fish.
Define "very sharp". I watch the LFS do 50% water changes on tanks full of Africans by going along and draining the water. Then going along and dumping in the buffer salts (the water here is extremely soft). Then going along and filling the tanks. Now most of these fish are in 40 gallon tanks. And there is a kH change of around 5-8 when the buffer salts are dropped into the tank. Then that kH goes down again when the fill water is adding. And with their water change system the fill takes about 2-3 minutes. So these fish are going though a quick rise in kH and pH and then a drop in kH and pH in a short amount of time. Yet they don't lose fish due to this.

But again. And I can't type slower than this. A normal pH changed caused by CO2 doesn't kill fish. Are you willing to concede that? You can drop the pH in an aquarium 1 (which gives 30 ppm of CO2) in minutes and not harm the fish. It's actually less of a change in pH than many fish have in the natural in a small stream with a tropical rain storm.
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Old 03-26-2007, 06:36 AM   #22 (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
CO2 doesn't deplete O2, not at night, not during the day, not at any time.
CO2 can displace O2, if you pump a bunch of it into the water column.
This can happen if 1) you're pumping excessive amounts of CO2, enough so that your filter's agitation of the water surface is the only thing keeping enough O2 in the water for the fish and 2) surface agitation stops long enough to stress the fish.

Lesson: Setup the tank w/ good filtration and very low surface agitation, then slowly bump up the CO2. This way, the fish don't get killed every time the filter craps out.

Related lesson/suggestion - Eheims are more reliable at restarting than Mags are.
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Old 03-26-2007, 07:19 AM   #23 (permalink)
 
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Default Re: Just wiped out a tank of fish

Here we go again! New contender. Round 2. Ding!

Last edited by Tonka; 03-26-2007 at 07:24 AM.. Reason: To be more funny....
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Old 03-26-2007, 07:38 AM   #24 (permalink)
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Default Re: Just wiped out a tank of fish

I'm not here for a fight, just stating that, under the wrong setup conditions (lots of filter induced surface agitation requiring a ton of CO2 injection to maintain 30ppm), it's possible for CO2 to displace enough O2 to cause fish troubles (when the filter craps out and the CO2 continues to get pumped into the now ~still water).

I don't see much to fight over here.

PS. CO2 is heavier than air, so if there is very little air movement in a room and enough of a gap between the top of the water & the top of the tank, you can build up too much CO2 at the surface (especially if you have the setup type I mentioned above). Have you ever seen soap bubbles floating on a cushion of CO2 in an aquarium? I have.

Last edited by Squawkbert; 03-26-2007 at 07:44 AM..
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Old 03-26-2007, 07:49 AM   #25 (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
Define "very sharp". I watch the LFS do 50% water changes on tanks full of Africans by going along and draining the water. Then going along and dumping in the buffer salts (the water here is extremely soft). Then going along and filling the tanks. Now most of these fish are in 40 gallon tanks. And there is a kH change of around 5-8 when the buffer salts are dropped into the tank. Then that kH goes down again when the fill water is adding. And with their water change system the fill takes about 2-3 minutes. So these fish are going though a quick rise in kH and pH and then a drop in kH and pH in a short amount of time. Yet they don't lose fish due to this.

But again. And I can't type slower than this. A normal pH changed caused by CO2 doesn't kill fish. Are you willing to concede that? You can drop the pH in an aquarium 1 (which gives 30 ppm of CO2) in minutes and not harm the fish. It's actually less of a change in pH than many fish have in the natural in a small stream with a tropical rain storm.

The OP said that a "dead hot magnum" caused high level of CO2 in the tank which killed the fish. I do not dispute the fact that a VERY high level of CO2 in the water column can kill fish. Normal CO2 level in air is ~350 ppm. 80 to 100 ppm in the water column is probably uncomfortable but not lethal to many healthy fish. Unfortunately, there is no way the CO2 level in the tank can go from a nominal of 20 to 30 ppm to above 200 ppm when the hot magnum fail...unless the tank has an exposed surface area of one square inch!

It is possible that the level of CO2 in the water column is already at the dangerous level with water circulation. When the pump fails, then the CO2 level can reach lethal level. This is a common failure mode among noobs (myself included when I first started CO2 injection). Inaccurate pH/KH readings can occur without good/calibrated test equipments.

CO2 death is often the result of a failed regulator/needle valve assembly. Noobs will also tell story about end-of-tank dumping. While it is true that the regulator may not be able to maintain the desired 15 psig at the outlet port when the tank is almost empty, the pressure rise is limited to about 50 to 70 psi, MAX! A quality needle valve with tapered needle and low Cv (flow coefficient) should not have any problem with this small increase in CO2 inlet pressure.

I use a Victor single-stage regulator and a brass Ideal 52 series -1- needle valve with 0.019 Cv (full open). It takes 20 turns to go from full shut-off to full-open. The valve is rated up to 3000 psig. Cheaper valves do not have full shut-off capability. If one cannot afford the $75 price tag, then go with the Fabco NV-55 valve. It's around 15 to 20 bucks with FULL taper needle for a bubble tight shut-off.

So do I run the tank to zero psi? Absolutely. Never had any problem with excessive CO2 level in the water column since 1996.

http://www.idealvalve.com/brassvalves.htm

"Normal" CO2 injection should not cause the pH to vary more than 0.8 point. This is safe for all aquatic inhabitants. However, a drop of 2 points can cause problem for aquatic life unless there exist a period of acclimation.
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Old 03-26-2007, 08:03 AM   #26 (permalink)
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Default Re: Just wiped out a tank of fish

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Originally Posted by Squawkbert View Post
CO2 can displace O2, if you pump a bunch of it into the water column.
This can happen if 1) you're pumping excessive amounts of CO2, enough so that your filter's agitation of the water surface is the only thing keeping enough O2 in the water for the fish and 2) surface agitation stops long enough to stress the fish.

Lesson: Setup the tank w/ good filtration and very low surface agitation, then slowly bump up the CO2. This way, the fish don't get killed every time the filter craps out.

Related lesson/suggestion - Eheims are more reliable at restarting than Mags are.
Again, these failure modes occur only when the CO2 level is already at the dangerous level with water circulation. I find 20 ppm to be more than sufficient to grow healthy plants. At 20 to 30 ppm of CO2, the lack of surface agitation cannot cause the CO2 level to reach lethal level!

The idiot proof method of adding CO2: directly into the intake filter. When the filter stops, then the flow of CO2 into the tank will also stop. No need to worry about surface agitation, water temperature, pH, KH, etc.
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Old 03-26-2007, 08:14 AM   #27 (permalink)
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Default Re: Just wiped out a tank of fish

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Originally Posted by Squawkbert View Post
I'm not here for a fight, just stating that, under the wrong setup conditions (lots of filter induced surface agitation requiring a ton of CO2 injection to maintain 30ppm), it's possible for CO2 to displace enough O2 to cause fish troubles (when the filter craps out and the CO2 continues to get pumped into the now ~still water).

I don't see much to fight over here.

PS. CO2 is heavier than air, so if there is very little air movement in a room and enough of a gap between the top of the water & the top of the tank, you can build up too much CO2 at the surface (especially if you have the setup type I mentioned above). Have you ever seen soap bubbles floating on a cushion of CO2 in an aquarium? I have.
Possible, but not achievable in the real world unless the tank has a surface area of only a few square inches. If the tank is not overstocked and there is a small opening at the top of the tank for gas exchange, then there will be sufficient O2 for the fish. Again, we're assuming that the initial CO2 level in the tank is 30 ppm.
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Old 03-26-2007, 08:52 AM   #28 (permalink)
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Default Re: Just wiped out a tank of fish

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Originally Posted by furballi View Post
Again, these failure modes occur only when the CO2 level is already at the dangerous level with water circulation. I find 20 ppm to be more than sufficient to grow healthy plants. At 20 to 30 ppm of CO2, the lack of surface agitation cannot cause the CO2 level to reach lethal level!

The idiot proof method of adding CO2: directly into the intake filter. When the filter stops, then the flow of CO2 into the tank will also stop. No need to worry about surface agitation, water temperature, pH, KH, etc.
Actually, given the failure mode I suggest, the CO2 level is not dangerous *until* water circulation stops because of power failure, filter death etc. If there's a balance between high surface agitation and high CO2 dosing, all is well until the balance is off, then CO2 rises and kills stuff.

Adding CO2 to the filter intake (assumption: you're talking about a canister filter) might buy you some time - if your dosing high amounts of CO2, you'll eventually fill the thing w/ CO2 and be pumping CO2 into the tank via the filter outlet. I suppose that, at least the CO2 entering the tank that way would be in the form of large bubbles, so it shouldn't raise the water's CO2 concentration as much. The surface agitation from breaking bubbles may even be adequate to prevent fish death.

Best approach: get CO2 dosing right in the forst place, set filter up for very modest surface agitation. Not only will this prevent major catastrophes, it saves $ spent on CO2.
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Old 03-26-2007, 09:21 AM   #29 (permalink)
 
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Talking Re: Just wiped out a tank of fish

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Originally Posted by Tonka View Post
By the way, its a great way to take inventory if you've lost track of what fish you have....
ROFL!!!!

Excellent thread BTW....
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Old 03-26-2007, 09:53 AM   #30 (permalink)
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Default Re: Just wiped out a tank of fish

I think we've got the theory covered, now let's try to figure out what happened to Benjavan.

Benjavan, can you describe your CO2 setup? How is your CO2 injected into your tank? Do you have an open top or a lid? Please try to be specific about your CO2 setup.
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