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**To**:**Aquatic-Plants at actwin_com****Subject**:**Re: Area for CO2 absorption****From**:**Paul Sears <psears at nrn1_NRCan.gc.ca>**- Date: Mon, 1 May 2000 11:12:54 -0400 (EDT)
- In-Reply-To: <200005010748.DAA03039 at actwin_com> from "Aquatic Plants Digest" at May 01, 2000 03:48:02 AM

> From: George Booth <booth at frii_com> > Subject: Re: CO2 Diffusion area > > >Date: Wed, 26 Apr 2000 22:58:33 -0500 > >From: "Dustin Swanson" <dustins at greatlakeseng_com> > > >I was wondering if there's a general formula or chart for the surface area > >of the CO2 in the "bell" that should come in contact with the water based on > >the size of the tank. > > There is such a table in "The Complete Book of Aquarium Plants" by Allgayer > and Teton. It shows surface area in cm^2 needed based on KH and tank volume > in liters. > > For a typical value of 5 dKH, surface areas are as follows: > > Volume: 1,000 800 600 400 200 100 > Area: 180 140 80 50 30 * > > For a value of 3 dKH, > > Volume: 1,000 800 600 400 200 100 > Area: 140 90 40 40 * * > > * CO2 produced by fish is sufficient under normal circumstances > > I had a go at this a few years ago. I reckoned (and still do) that the important thing wasn't the volume of the tank but the surface area. If the normal equilibrium value of CO2 in water (in air) is about 0.5 ppm, let's suppose we want about 40 times that, or 20 ppm. We originally had the full area of the tank at 330 ppm CO2 in the gas, and we are going instead to use a smaller area at 1000000 ppm. The gas concentration increase is 1000000/330 or about 3030, and we actually wanted forty times as much in the water, so we can use 40/3030 or about 1/75 of the surface of the tank. My 160 L has a surface of about 3600 cm^2, so I need about 3600/75 = 48 cm^2 of bell area. This is in the same ballpark as the numbers above. I actually use a smaller area of highly agitated water (faster transfer), and it seems to work. Someday I'll try to model this a bit more rigorously, but surface transfer effects are not the easiest of things to model! -- Paul Sears Ottawa, Canada

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