Calling all scientists - Re: dissolving air in co2 reactor - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 07-16-2015, 11:33 PM Thread Starter
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Calling all scientists - Re: dissolving air in co2 reactor

Hi guys,

Excuse my use of a layman term: Scientists.

I have a question: I have a Cerges co2 reactor that I want to use to dissolve some air (source: air pump) with during the night. I will have a timer to turn on the air pump for several seconds to fill the co2 chamber so that the reactor will not over-fill and de-prime. That said, my co2 isn't on a timer, it will pump 24/7.

My question is whether or not this will work.

Please advise. Thanks
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post #2 of 13 (permalink) Old 07-17-2015, 12:19 AM
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If your goal is to not gas your fish you would be better off to use the timer on the co2 and forget the air pump. If you need to add a solenoid to your co2 system they are pretty cheap.

I doubt that the o2 level will rise enough to make a difference, especially if your co2 does not shut off. If you ran an airstone in the tank rather than in the reactor it would both dissolve o2 and drive off co2 creating a better environment for both fish and plants.

Putting a solenoid on your system is going to save money on refills and will pay for itself in a year or so in wasted gas alone.
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post #3 of 13 (permalink) Old 07-17-2015, 12:21 AM
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Not sure what your trying to accomplish here? Assuming your trying to add oxygen at night to prevent the fish from being gassed out? Can you put the CO2 on a timer and turn it off at night? If not I'd just add an air stone and leave the reactor alone.


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post #4 of 13 (permalink) Old 07-17-2015, 12:32 AM
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Dissolved oxygen and CO2 could both be present in a reactor and be maintained in the water column.
Reactor may need to be larger, water GPH, etc.. should all be considered.

My question is what is your goal here.


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Growing is not that difficult.
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post #5 of 13 (permalink) Old 07-17-2015, 02:42 AM
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Air is only about 20% oxygen. Oxygen is much harder to dissolve in water than CO2 is. A reactor which works with CO2 is very unlikely to be at all effective for dissolving more oxygen into the water. As the others pointed out, it will work far better to use an airstone in the tank at night, with the CO2 shut off. That airstone increases the water surface movement, and most of the oxygen the tank water picks up comes from the water surface, not the air bubbles from the airstone.

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post #6 of 13 (permalink) Old 07-17-2015, 03:14 AM
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Exactly.

The benefit of surface boil is the escape of co2 from soln moreso than the taking on of extra o2 into the water under typical temps and pressure. Bubbling a sample of water doesn't increase o2 retention greatly, it facilitates offgassing of co2 which is beneficial in some biomes and limiter to others

To get done what you are wanting, pressure and temp modification would be req

Imo your tank 99.9% likely already has fine o2 levels if its not packed with years of untended waste, and depending on what you want to accomplish sometimes simply shutting of co2 at the right time or facilitating its escape gets the same ends

The single best way I know to maintain over 100% o2 saturation at typical temps and pressure is to input plants, co2 and bright light and ferts and enjoy the natural bubbling long about 3 pm heh

small old reef tank:

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post #7 of 13 (permalink) Old 07-17-2015, 03:57 AM Thread Starter
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Okay thanks guys.

In terms of what I'm trying to accomplish, I just want to see if extra o2 injection will have any effect on plant growth.
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post #8 of 13 (permalink) Old 07-17-2015, 02:12 PM
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Quote:
Originally Posted by chinaboy1021 View Post
Okay thanks guys.

In terms of what I'm trying to accomplish, I just want to see if extra o2 injection will have any effect on plant growth.
Has anyone actually measured dissolved O2 concentrations in a tank with an airstone vs without? With all the surface agitation, I don't think an air stone would actually do anything except off gas any extra CO2 thats pumped in.
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post #9 of 13 (permalink) Old 07-17-2015, 07:44 PM
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Originally Posted by Virc003 View Post
Has anyone actually measured dissolved O2 concentrations in a tank with an airstone vs without? With all the surface agitation, I don't think an air stone would actually do anything except off gas any extra CO2 thats pumped in.
If the water surface of an aquarium is still, its area is the cross section of the tank. But, if you get the surface to ripple a bit, with an airstone, or by directing a powerhead so it ripples the surface, the area of the water surface can be as much as 50% bigger (crude guess), from the troughs and valleys. Oxygen in contact with the water surface is slowly absorbed by the water in proportion to the area of the surface, so an airstone will lead to more oxygen in the water.

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post #10 of 13 (permalink) Old 07-17-2015, 07:53 PM
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I have wondered about the same thing. If we could inject o2 similar to how we inject co2 would that have any benefits. With surface agitation it helps increase o2 but would also off gas some co2. If we added a port into say a rex grigg reactor and were able to control the amount of o2 being dissolved so when the water entered back into the tank there were no bubbles, would this be benefical?

My gut says yes it would be beneficial but we would probably not see any real world benefits.
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post #11 of 13 (permalink) Old 07-17-2015, 08:09 PM
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Note that CO2 is about 40 times as soluble in water as oxygen. That means it is much, much easier to dissolve CO2 from the atmosphere, than it is to dissolve oxygen from the atmosphere into our aquariums.

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post #12 of 13 (permalink) Old 07-17-2015, 08:16 PM
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Quote:
Originally Posted by Hoppy View Post
If the water surface of an aquarium is still, its area is the cross section of the tank. But, if you get the surface to ripple a bit, with an airstone, or by directing a powerhead so it ripples the surface, the area of the water surface can be as much as 50% bigger (crude guess), from the troughs and valleys. Oxygen in contact with the water surface is slowly absorbed by the water in proportion to the area of the surface, so an airstone will lead to more oxygen in the water.
This is probably insignificant, and will only be a factor if you assume that the water at the immediate surface starts at significantly lower oxygen concentration than the saturation point. This is unlikely to ever happen, and the much larger barrier to oxygen diffusion throughout the whole tank is the water itself.

In this context, water at the bottom of the tank is much more likely to be non-saturated. Bubbles from the air stone generate currents that bring this water to the surface, where it can become saturated. Most other forms of filtration/circulation have the exact same effect.

I should also add that if you were to somehow just add oxygen/air without water movement, the change in surface area is again going to be insignificant. Whereas you could bubble nitrogen through an airstone and still get a big improvement in overall oxygen levels.
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post #13 of 13 (permalink) Old 07-18-2015, 10:09 AM
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In a planted tank, just add more CO2. Magical things happen when the plants strip the Carbon atom.
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