I am so torn....lives plants or not - Page 3 - Tropical Fish Keeping - Aquarium fish care and resources
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post #21 of 24 Old 01-29-2010, 12:47 AM
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I've recently read about what you are inquiring about Holly and Byron is right on. When the water surface is agitated it "churns" air which contains o2 into the water displacing the co2 which is needed by the plants. Same as if an air stone is added. It displaces the co2. You want your plants to make the o2 for the fish to breathe and you want the plants to consume the co2. Introducing more o2 by air stone, surface agitation, etc... starves the plants for what they need as it gases off the co2 too fast.

“He who knows nothing is closer to the truth than he whose mind is filled with falsehoods and errors”
Thomas Jefferson quote
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post #22 of 24 Old 01-29-2010, 11:28 AM
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I tried to explain this on another post but I didn't do a very good job. But basically the following is true:
- Both air and water can hold varying amounts of O2 & CO2.
- Water and air exchange O2 & CO2 at the water’s surface.
- The larger the air to water surface area, the faster the exchange can take place. The more water movement the faster the exchange.
- There's an equilibrium point for O2 & CO2 between the water and air. This is the hard part to explain.

So to keep this simple, let's say that water and air to be equalized or "balanced" each hold 10ppm of CO2. If you were to have a tank with no plants, just fish, the level of CO2 in the water would go higher than 10ppm because of the fish respiration. Now let’s assume the waters CO2 level is at 15ppm. At the water’s surface, the water would be trying to give up the extra CO2 because the air has less. Between the water and air, they would be trying to balance the levels out again so the two match.
Now lets' assume a planted tank with few fish. Although the fish are give off CO2, let's assume the plants are using it up faster than the fish can produce it. So now let assume the water has a CO2 level of 8ppm. At the water’s surface, it would now get absorbing CO2 from the air to replenish its level until it equaled the airs level.
This same example hold true for O2 as well.
Now the amounts of CO2 I used in the above example are not the exact figures. I think air has about 380 PPM of CO2 compared to less than 10ppm for water. And they don’t match exactly. But the bottom line is there’s an equilibrium point between the two. And if you have higher amounts of CO2 in the water and don’t want it to expel into the air, you’d want to reduce water movement. If you have low levels of O2 in the water and you want to increase it, you’d want to encourage the exchange by increasing the water movement.
Carbon Dioxide in the Ocean and Atmosphere - sea, depth, oceans, important, system, plants, marine, oxygen, human, Pacific
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post #23 of 24 Old 01-29-2010, 01:36 PM
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I knew in the back of my mind there had been something good posted about this. Thanks WisFish for reposting your explanation here. B.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #24 of 24 Old 01-30-2010, 11:37 PM Thread Starter
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Thanks guys! I will post again soon on this. I am too pooped right now.
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