# Water Movement/CO2 Degassing



## dwalstad (Apr 14, 2006)

Here's a recent, interesting question that I received:

_The one thing that keeps cropping up is how much surface agitation should one have in these tanks. I keep wondering at what point this surface movement expels the Co2 rather than oxygenates. I guess its quite a fine line.

I am now just using very small internal filters with no filter media for circulation.

Do you think that provided the flow from these pumps doesn't actually break the surface, (causing splashing) the Co2 content would be largely unaffected. _

I think that the water movement you're using (internal pumps without surface agitation) is good for plants and the aquarium ecosystem. I also use internal filters that simply circulate water. Water movement is good-- brings nutrients to plants, aerates the water, helps keep the substrate from become severely anaerobic, and stimulates bacterial activity. More bacterial activity means more CO2 generated for plants and the more rapid processing of fish wastes into plant nutrients.

Any kind of air bubbling and water surface agitation will bring oxygen into the water. But it will also degass CO2. The more surface agitation, the more CO2 lost. CO2 is the one nutrient that plants need most, and its the one that can be so easily lost from the tank. CO2 degassing may also bring the pH up, making it even harder for plants to get CO2.

Thus, I would avoid vigorous bubbling from airstones or a lot of water splashing from Hang-on-the-Back filters. Let fish behavior guide you. Unless the fish are having breathing problems, turn down those air-pumps and splashy filters. Check fish in the early morning (before plant photosynthesis kicks in oxygen) for unusual lethargy or gasping at the surface.

In a new tank with a fresh organic soil, the soil will generate a LOT of CO2. As time goes on, this CO2 production lessens. Thus, surface agitation may be fine and/or necessary for the first 6 months. As the soil stabilizes, less water aeration is needed and CO2 degassing becomes increasingly more of a problem.

So you're right, there's a _Fine Line_ between degassing out all CO2 and providing enough oxygen to fuel the ecosystem. Furtheremore, where this line is changes as the tank establishes itself.


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## EMc/ (Feb 20, 2006)

This is an interesting question & one I've been considering more & more these days. I currently don't use anything mechanical to help circulate water. I figured the fish provided water circulation. If you keep fairly inactive fish, this won't work & is probably the reason (or one of them) that plants don't do as well in my betta coccina tank. They are shy & do a lot of hiding. When out, they just glide slowly around hunting. But in all the rest of my community tanks, there is a lot of activity, usually in all levels. 

I had been hearing that you (Diana) advocated some water circulation to improve nutrient distribution, but I didn't realize you also mean for the surface to not be agitated. There are times, when it gets very hot in the summer, in our office (where I also have tanks) that I have added an over the back filter to help dissipate heat from the water. Unfortunately, in the tank(s) that need(s) increased water circulation to help displace heat, I guess the over the back box filters are more effective in doing this. And, looking back, I didn't ever notice improved plant growth when I would add those. I guess I was displacing too much CO2. 

I think I will try a small internal filter for that betta tank, but will need to research them, as I am not familiar w/ them. 

Thanks,

Marty


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## dwalstad (Apr 14, 2006)

My two shrimp bowls have been getting great plant growth with no water circulation. And the movement of 4 shrimp/bowl doesn't make much of a current.


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## Red_Rose (Mar 18, 2007)

It is possible to use HOB filters and not end up with surface agitation from them. If you use a baffle, you can easily use a HOB and not have to worry about water splashing about. I have an AquaClear 20 in my betta's 10g tank and there is no surface agitation whatsoever. The great thing about using a baffle with these filters is that your floating plants won't be constantly moving all around. They will actually stay in place.


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## bartoli (May 8, 2006)

Red_Rose said:


> It is possible to use HOB filters and not end up with surface agitation from them. If you use a baffle


Although I no longer use any HOB, I think the idea of using a baffle is great! One concern with making a baffle out of water bottle is the leaching of polycarbonates.


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## dwalstad (Apr 14, 2006)

Red Rose,

Thank you for the link about baffles. Very clever idea!


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## Red_Rose (Mar 18, 2007)

You're welcome! The only reason I know about it is because I did a lot of searching on what I could do to try to lessen the flow of a filter for bettas. While this baffle really doesn't slow down the current, it does make it easier for fish who don't like strong currents.



bartoli said:


> One concern with making a baffle out of water bottle is the leaching of polycarbonates.


What would polycarbonates do if they were to leak into the water? The only reason I ask is because I know there are a lot of people who use this for betta tanks(or for any small fish that can't handle strong currents) and I've never heard of any complaints from them.

Also, if you'd rather not use plastic from a soda or water bottle, there is a way to make one out of acrylic. I came across someone who makes baffles out of acrylic on LiveJournal but I'd just have to find that entry. I'll post it when I find it for those who may be interested in it. 

EDIT: Here's the link.


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## dwalstad (Apr 14, 2006)

Red_Rose said:


> What would polycarbonates do if they were to leak into the water? The only reason I ask is because I know there are a lot of people who use this for betta tanks(or for any small fish that can't handle strong currents) and I've never heard of any complaints from them.
> QUOTE]
> 
> I don't expect you'll _ever_ hear complaints from Betta breeders about their polycarbonate baffles. I took a quick look at this website:
> ...


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## bartoli (May 8, 2006)

Red_Rose said:


> What would polycarbonates do if they were to leak into the water? The only reason I ask is because I know there are a lot of people who use this for betta tanks(or for any small fish that can't handle strong currents) and I've never heard of any complaints from them.


Red Rose, thank you for the link on using acrylic.

Back in Aug/2007, there was an article (from medicinenet.com) saying that researchers had discovered a biological mechanism allowing bisphenol-A to be absorbed by breast cancer cells. (Although I still have a copy of that article, I cannot give you a link - the article is no longer on-line.) The article was referring to a study published in the Aug. 28 issue of Chemistry & Biology. Prior to that discovery, people thought BPA was safe.

About a year later, in 2008, the Canadian federal government was looking into banning polycarbonate baby bottles:

http://www.cbc.ca/canada/story/2008/04/18/bisphenol-a.html

"We have concluded that early development is sensitive to the effects of bisphenol A. Although our science tells us that exposure levels to newborns and infants are below levels that cause effects, we believe the current safety margin needs to be higher."

Of course, the industry heavily objected to that.


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## Evil-Lynn (Apr 6, 2009)

dwalstad said:


> My two shrimp bowls have been getting great plant growth with no water circulation. And the movement of 4 shrimp/bowl doesn't make much of a current.


Diana,
If there is no water movement at all in your bowls and you experience good plant growth, could it be that your plants are getting most of the oxygen they need from the air in the surface as opposed to the water? It looks like many of them have reached the surface, emerging from the water.


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## dwalstad (Apr 14, 2006)

Evil-Lynn said:


> Diana,
> If there is no water movement at all in your bowls and you experience good plant growth, could it be that your plants are getting most of the oxygen they need from the air in the surface as opposed to the water? It looks like many of them have reached the surface, emerging from the water.


Evil-Lynn,

Please consider that plants need CO2 much more than oxygen. For plants, oxygen is a "waste product" of photosynthesis.

The submerged plants are getting the CO2 they need from decomposition of soil organic matter. The emergent plants are getting the CO2 they need from air, which is generally a better CO2 source than water.

Its all in my book.


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## Supercoley1 (May 28, 2007)

I don't understand the theory of de gassing here!!!

If CO2 has a natural equilibrium in water then having surface turbulence will not degass nor bring in more CO2. In reality some leaves but is replenished but it will maintain it's equilibrium.

degassing occurs when we inject more than equilbrium and therefore is trying to return to equilibrium.

I add a lot of surface turbulence to my non CO2 tank to bring in more O and also to replenish CO2 use back to the equilibrium quicker.

AC


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## Juergen (Sep 5, 2008)

the equilibrium exists only at the water/atmosphere border and should be around 0.5-1mg/l CO2 in water.
Higher CO2 levels can be achieved in water layers that have no atmospheric contact.
Or in other words...if water has a beyond the equilibrium level of CO2, maybe because of natural CO2 production in the tank or CO2 injection, almost everything of that CO2 is lost, if that peticular amount of water is allowed to have air contact a while.
Airstones are very good in stirring up the water around the tank and lift lots of water to the surface.
In contrary electrical pumps move lots of water too - maybe even more, but it is not guaranteed that those 'mighty streams' make atmospheric contact.
Parts of them may only circulate water in deeper layers and lead to lesser gas exchange at the water surface.
Plant people usually want CO2 concentrations of 10-20mg/l, much more than the equilibrium can provide.
regards


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## dwalstad (Apr 14, 2006)

Supercoley1 said:


> I don't understand the theory of de gassing here!!!
> 
> If CO2 has a natural equilibrium in water then having surface turbulence will not degass nor bring in more CO2. In reality some leaves but is replenished but it will maintain it's equilibrium.
> 
> ...


NPTs often have considerable CO2 in the water-- just as in natural rivers and streams (see my book, p. 100). The CO2 is produced by the decomposition of organic matter by bacteria. There may not be as much CO2 as in a High Tech tank receiving artificial CO2 injection, but there is _much_ more than the 0.5 mg/l produced by equilibrium with the atmosphere. In a new tank with an organic soil, I believe that CO2 levels compare to High Tech tanks. Unfortunately, hobbyists that don't understand the role of decomposition in aquarium ecology, degas it all away. So sad. 

When you aerate the water in an NPT, you are indeed removing (degassing) CO2. This could slow plant growth substantially making it impossible for plants to produce enough oxygen for fish. My advice has always been to use as little mechanical aeration as possible. Let fish behavior be your guide (my book, p. 73).


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## Supercoley1 (May 28, 2007)

Juergen said:


> the equilibrium exists only at the water/atmosphere border and should be around 0.5-1mg/l CO2 in water.
> Higher CO2 levels can be achieved in water layers that have no atmospheric contact.


It is my understanding that this 0.5mg/l is in sterile water and that in non sterile water is more likely to be in the 3 - 8ppm range. Of course this depends on water temperature too.



> Plant people usually want CO2 concentrations of 10-20mg/l, much more than the equilibrium can provide.


My other tank has CO2 injected to 30-35ppm+ and I have even more surface turbulence on this tank than I do on the non CO2 one. I inject a little more to compensate.



> The CO2 is produced by the decomposition of organic matter by bacteria.


What if there is no decomposition? There is little livestock in the non CO2 and there is no plant decomposition  This is even with me having the spray bar move the water surface. The filter has a throughput of 20x the tank volume so it is pretty considerable water movement within the tank and at the surface.



> Let fish behavior be your guide


Indeed good advice  This non CO2 tank with zero water changes and small doses of KNO3 and KH2PO4 weekly is my Cory Fry and Cherry Shrimp tank and they are all very happy 

AC


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## Juergen (Sep 5, 2008)

Supercoley1 said:


> It is my understanding that this 0.5mg/l is in sterile water and that in non sterile water is more likely to be in the 3 - 8ppm range.


hm, is there any online reference for this you can point me to?
Or maybe you can take a scan or digipic, if you have a printed refererence? 
regards


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## dwalstad (Apr 14, 2006)

Supercoley1 said:


> What if there is no decomposition?


It there is food, there will be decomposition. If there is decomposition, there will be CO2.


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## Supercoley1 (May 28, 2007)

Juergen said:


> hm, is there any online reference for this you can point me to?
> Or maybe you can take a scan or digipic, if you have a printed refererence?
> regards


I shall have a look for something. Not something I ever looked into, rather something remembered from researching other things. Be patient 



> It there is food, there will be decomposition. If there is decomposition, there will be CO2.


Point taken  I do feed the fry although not much that will provide some decomposition. 

AC


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## filedor.com (Jun 2, 2012)

dwalstad said:


> When you aerate the water in an NPT, you are indeed removing (degassing) CO2. This could slow plant growth substantially making it impossible for plants to produce enough oxygen for fish. My advice has always been to use as little mechanical aeration as possible. Let fish behavior be your guide (my book, p. 73).


I'm sorry to retake this topic, but before I ask my question let me tell Diana how much I admire you , your book is like my bible I have been reading it everyday since I bought it. I live in Korea (but I'm Panamanian), I can buy as many plants I want here so I'm taking my time to build a very nice "Diana Walstad" fish tank, but I want to try something else, I want to make a "Diana Walstad"-based Refugium, people asked me "why do you want to have a refugium? just get a bigger tank...", but I have an easy answer for that "I don't want duckweed in my main tank, and I have a huge java fern which works like a miracle, and a nice Echinodorus but these two plants are too big for my 20 gal tank and I also want to put my heater in the Refugium" now my dilemma is about the water surface agitation and water movement. I know I cannot use spray bars... but how about just putting the outtake tube from my refugium just into the water to create a water flow which will produce some water movement. I don't know if I get the point, and I couldn't totally understand it from the book, but, can I actually depend on just plants for fish oxygen? (in heavily planted tank) or can I still have a little bit of water agitation, probably a tube dropping water around 1cm away from the surface? or should I just put the tube directly inside of the fish tank? What about your HOB, the waterfall probably is splashing a little bit, right? or is the water level just like 1cm away from the waterfall?

I will also post my refugium idea here. I will have a pvc overflow, (double intake model) and the outtake tube from my refugium going to my main tank, I'm still not sure how should this tube be... _a spray bar 1 cm away from the surface? a tube 1 cm away from the surface? a tube same level from the surface? or a tube right into the water?_


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