newbie question on flow

aquabillpers

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Carissa;27971 said:
Airstones are fine for non-co2 tanks that are small (like 20g or less). They help keep co2 levels stable in that type of environment, and provide some extra circulation in a tank with a very small water volume. But in a larger tank, or one that is co2 injected, a powerhead is a better idea.

guy tillmans;28591 said:
i am probably mistaken, but heavy waterflow is only important in a hightech tank, when it's a low tech tank you don't need a powerhead.

CO2 is always in short supply in non-injected tanks, so any water movement that drives it out should be avoided. That includes any fixtures that cause a lot of surface agitation. Properly-sized airstones work fine in smaller tanks.

However, some water flow is needed in such environments to distribute nutrients. I use a small HOB filter which seems to do the job without a lot of surface disturbance; a small submersible pump, properly aimed, will work well as long as it didn't create a lot turbulence.

Bill
 

SpeedEuphoria

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you want good surface agitation in non co2 setups b/c then the co2 levels will stay around ambient and not fall and rise
 

aquabillpers

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SpeedEuphoria;28642 said:
you want good surface agitation in non co2 setups b/c then the co2 levels will stay around ambient and not fall and rise

I believe that water absorbs CO2 from the atmosphere at a much lower rate than it does oxygen, for example. A non-injected tank with a lot of surface agitation would therefore have a lower average level of CO2 than one with no agitation.

Bill
 

VaughnH

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Water absorbs CO2 much more readily than it absorbs oxygen, as far as I have been able to learn. So, I agree that having good surface water movement is the best way to keep some CO2 in the water in non-CO2 tanks. While the concentration of CO2 in air is very low, compared to oxygen, CO2 goes into solution in water much more easily than oxygen. Water will dissolve orders of magnitude more CO2 than oxygen. I would google this, but I can't think of a good way to do so.
 

aquabillpers

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VaughnH;28647 said:
Water absorbs CO2 much more readily than it absorbs oxygen, as far as I have been able to learn. So, I agree that having good surface water movement is the best way to keep some CO2 in the water in non-CO2 tanks. While the concentration of CO2 in air is very low, compared to oxygen, CO2 goes into solution in water much more easily than oxygen. Water will dissolve orders of magnitude more CO2 than oxygen. I would google this, but I can't think of a good way to do so.

I couldn't find anything on CO2 absorption either. I know I read something several years ago (probably at APD) that claimed that CO2 was much less readily absorbed by water than O2, but that could have been incorrect.

I also have the impression that CO2 is outgassed from water at a faster rate than it is absorbed, but I'm not sure. I'm going to start a thread on that.

If you are really suggesting that having strong surface agitation is a good way to keep CO2 in the water of a non-injected tank, you are disagreeing with Barr, Walstad, and many others. They maintain just the opposite.

But disagreement is good for the brain, too.

Bill
 

VaughnH

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Disagreement is how I keep my blood circulating!

I do know that water will dissolve far more CO2 than oxygen, and, as I recall, it dissolves about 1000 times more. If you start with water and air at equilibium as far as CO2 concentration is concerned, the rate of gain of CO2 from the air has to be equal to the rate of loss of CO2 from the water. That is what being in equilibrium means.

For many years people used air bubblers in fish only tanks to keep oxygen dissolved in the water, mostly by rippling the water surface. CO2 was not even a consideration at that time, since fish generate so little of it, it doesn't matter if you get rid of it fast or slow. But, you can't increase the surface area of a body of water, which ripples do, without increasing the rate of absorbing CO2 from the air at the same time, at least until the water and air concentrations are in equilibrium. And, if you aren't injecting CO2 into the water, there is none there, beyond what is absorbed from the air, to be lost to the air. Without CO2 in the water plants have to get C from organic carbon compounds.

Now, I await the disagreements!
 

Carissa

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Here's the way I've always thought about it. CO2 must get absorbed into the water from the air. If it doesn't, there's theoretically none in the tank unless you just did a water change. Circulating the water will only cause the water to come to a greater equilibrium with the atmosphere, it won't do anything special to the water to make it less likely to absorb co2 from what I understand. So once the plants have used up all the co2 assuming no absorption from the atmosphere, which would happen quickly in a non-co2 tank, where is the co2 going to come from? If it's getting driven off faster than it's getting absorbed, to me that means that it's not at equilibrium to start with. But if you start with a tank with no co2, which is what would happen in a tank with plants that are using it, you can only gain from that point.

The only thing that maybe would change matters is if you have fish producing enough co2 themselves to keep the co2 concentration above equilibrium. I'm not so sure that fish really produce enough co2 to do this, considering how quickly plants can use up co2.

My own anecdotal experience seems to bear out that more circulation increases co2 levels in a non-co2 tank. I had a tank that started having bba issues. After I added more circulation and cleaned out the bba, I never had a recurrence. This would lead me to think that co2 was getting depleted and causing the bba (since co2 is usually the main culprit in bba outbreaks), and adding the circulation evened out the amount of co2 in the tank at any given time. I also saw a good increase in the health of the plants after adding more circulation. I can't prove that it was co2 related but this theory would explain everything that took place.
 

aquabillpers

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Hi, Carissa,

It has been often noted that algae and poor plant growth can be caused by poor circulation of the water in an aquarium, even though CO2 and other nutrients that are supplied are adequate. That's why overgrown tanks (like most of mine) develop problems.

Could your success with the BBA be due to the fact that you were dispersing the nutrients better, due to the increased agitation?

There are many postings on the internet that say that surface agitation drives off CO2. The consensus seems to be unanimous, although I didn't read all of the 7,400 returns. :)

Bill
 

VaughnH

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aquabillpers;28657 said:
Hi, Carissa,

It has been often noted that algae and poor plant growth can be caused by poor circulation of the water in an aquarium, even though CO2 and other nutrients that are supplied are adequate. That's why overgrown tanks (like most of mine) develop problems.

Could your success with the BBA be due to the fact that you were dispersing the nutrients better, due to the increased agitation?

There are many postings on the internet that say that surface agitation drives off CO2. The consensus seems to be unanimous, although I didn't read all of the 7,400 returns. :)

Bill

Those 7400 aquatic plant experts are all correct - surface agitation does drive off CO2, but only if there is more CO2 in the water than would be there in equilibrium with the air. If there isn't more CO2 in the water than the equilibrium amount, surface agitation cannot drive off the CO2, but can increase the amount absorbed by the water from the air.

People who discuss driving off CO2 from the water are universally people who are trying to build up CO2 in the water, by injecting it somehow. People who don't add CO2 to the water won't be discussing CO2 at all, except perhaps to crow about how much simpler their life is.
 

SpeedEuphoria

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aquabillpers;28646 said:
A non-injected tank with a lot of surface agitation would therefore have a lower average level of CO2 than one with no agitation.

Bill
This doesnt make sense to me. You must be assuming that all the CO2 comes from fish in a non injected tank? Your also assuming that surface agitation only off gasses CO2.

aquabillpers;28652 said:
If you are really suggesting that having strong surface agitation is a good way to keep CO2 in the water of a non-injected tank, you are disagreeing with Barr, Walstad, and many others. They maintain just the opposite.
Please post links to where they state this, as I have never seen it. I think you are misinterpreting what they say.

In a CO2 injected tank, surface agitation off gasses CO2 because the atmospheric levels are lower than the water. The surface agitation tries to balance the levels, same thing in non injected IMO, it will try to balance to atmospheric by adding CO2.

Edit was doing some research and found a great article for info, so far starting on page 7 has good info:
http://www.ieagreen.org.uk/oceanrep.pdf

also this one has good info
http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/14_4/14_4_feely_et_al.pdf

The CO2 uptake rate depends on the PH and temp
 

Carissa

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^ my thoughts exactly. If agitation only drives off co2, that means that true equilibrium is actually 0 and the only way to get any co2 at all is to add it in some way, either via fish or injection. If that were the case, the amount of co2 that fish provide should cause wild pH fluctuations as soon as fish are added to an otherwise empty tank. Reason being that an increase in the amount of co2 10x will lower the pH by 1.0. So if we assume that we are starting near 0 ppm of co2, adding even a tiny amount of co2 (like 0.5 ppm) should lower pH by 1.0 or more, if I understand the formula correctly. I've never heard stated that circulation drives off co2 in a non-co2 injected tank, in fact I've only heard the opposite in conjunction with any reasoning to back it up.

As far as the additional circulation goes in my non-co2 tank, yes, I know that it's not conclusive proof that circulation increases co2. But the fact that bba almost always and almost exclusively starts as a result of co2 fluctuations (specifically reduction), points me to the logical conclusion that co2 levels must have increased to cause the problem to go away.
 

aquabillpers

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In what is called a "Natural Planted Tank" supplemental CO2 comes mainly from decomposition in the soil substrate and of fish waste and detritus. In such a tank, without surface agitation the CO2 level is higher than that in the local atmosphere. That excess is driven off by surface agitation, and that is to be avoided in such a tank.

In a natural body of water it is not unheard of to find the CO2 level to be higher than ambient, because of decomposition.

That process is described in some detail in Diane Walstad's "Ecology of the Planted aquarium", on pages 59 and 60 and page 100 and 101 in the first edition. IMO, this book should be read by everybody who grows aquatic plans, whether in a high tech or low tech environment.

There are many other references on the web. There is also a forum at APD for those who want to learn more about NPT's. http://www.aquaticplantcentral.com/forumapc/el-natural/

Bill
 

Tom Barr

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In many areas I've found about 2-4 x the ambient levels of CO2 right at the water's surface, suggesting CO2 evolving from the swamps. At lower levels, this makes a large difference since CO2 is the most limiting of any "nutrient" for submersed plants.

I have reduced flows in non CO2 tanks, maybe 5x per hour vs 10-15x per hour in the CO2 enriched tanks.

Regards,
Tom Barr
 

Carissa

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But would this apply to a regular, non-co2 tank (not soil substrate)? I wasn't really thinking about NPT's, but now that I think about it I do remember hearing about the breakdown of certain substances producing carbon for the plants. But I had thought that this only applied to NPT's.
 

crystalview

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I understand the more flow thing, thanks to the above posts. Been looking at the Nano.
I noticed that two of the posts say they have two filters on their tanks, which are about the size of mine (tank and filter). Can you explain the reason for this? I have one and so far (6mo) the water is stable in quality. Wouldn't both of those filters give the tank more flow without really needing a powerhead? I have another filter but thought the one was suffient. So what is the reasoning for 2 filters, more bio-load?