# How much surface agitation?



## bjorn (5 Apr 2011)

How much surface agitation should you have on a planted tank with pressurized CO2? I can see a big difference in CO2 being lost when I have lily pipes slightly raised. Is it still supposed to be better to have the surface completely still?


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## ceg4048 (5 Apr 2011)

Please review viewtopic.php?f=37&t=13899

Cheers,


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## bjorn (5 Apr 2011)

ceg4048 said:
			
		

> Please review viewtopic.php?f=37&t=13899
> 
> Cheers,



Yeah I read that, but it doesn't quite answer my question. I do understand that Co2 will dissipate with too much surface movement, but could it also be benefical to have more O2 mixed into the tank and compensate by injecting a bit more CO2?

For example, if I have more O2 entering the water column, would the fish not be able to cope with a higher amount of CO2 dissolved in the water? 

Or is it better to preserve as much CO2 as possible and not worry about O2? Are there any benefits from having more ripples rather than less (but lose CO2 quicker)?


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## ceg4048 (5 Apr 2011)

Well, it's important to understand that plants oxygenate the water more than what can be achieved by aeration alone. Whatever concentration of gas is dissolved in water, if you agitate the water then that gas moves from the water to the atmosphere, not the reverse. Therefore, if you agitate the water too much in a CO2 injected tank then you lose both CO2 and O2. Since there is a direct relationship between the CO2 concentration level and the O2 production then excessive agitation will not only cause direct out-gassing of the O2, but due to CO2 loss will then attenuate O2 production, which is a double whammy. 



			
				bjorn said:
			
		

> For example, if I have more O2 entering the water column, would the fish not be able to cope with a higher amount of CO2 dissolved in the water?


There is very little compensation that can be achieved by increasing the O2 content of the water in relation to this function. The effect of CO2 in the fishes bloodstream has to do with acidification of the blood, which then affects the ability of hemoglobin in the blood to hold onto, and to transport the O2 molecules. This is the cruel irony of CO2 toxicity (hypercapnia). There is no shortage of O2, but there is a loss of ability of the hemoglobin to bind to the O2. This is not a fault of hemoglobin. It's actually how the O2 binding mechanism is supposed to work. 

When blood enters tissue that is high in metabolic waste, the pH in that tissue is low due to CO2 produced by that tissue. The acidity causes the hemoglobin to drop it's payload of O2 and to collect CO2. The blood then travels to the gills where the pH is normally higher. At higher pH the affinity for O2 is high, so the hemoglobin unloads it's payload of CO2 where it diffuses out through the gills and then uploads O2 to start the cycle all over again. If the CO2 concentration of the water is high then the CO2 cannot escape from the fish and the blood pH drops, signaling the hemoglobin to drop it's payload of O2 at the wrong location.

Only the fishes system has the ability to buffer the acid by elevating the levels of bicarbonate (HCO3) thereby raising the pH and restoring the hemoglobin's affinity for O2.



			
				bjorn said:
			
		

> Or is it better to preserve as much CO2 as possible and not worry about O2? Are there any benefits from having more ripples rather than less (but lose CO2 quicker)?


Find an agitation level that is a good compromise between keeping a clean scum-free surface and keeps healthy fish but which also retains sufficient CO2 to accomplish the goal of adequate growth.

Cheers,


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## bjorn (5 Apr 2011)

Got it thanks! I understand now. I was just experimenting a bit before and noticed that even a slight increase of surface movement from what I normally have, causes a lot of CO2 to disappear.

And how do you know so much?  Seems you know everything from Chemistry to Biology in detail so well!!


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## ceg4048 (6 Apr 2011)

bjorn said:
			
		

> Got it thanks! I understand now. I was just experimenting a bit before and noticed that even a slight increase of surface movement from what I normally have, causes a lot of CO2 to disappear.


This is another reason I dislike lily pipes and other single point filter outflow devices. They may look pretty but they don't function as well as spraybars for surface agitation. If you create bubbles, foam, or in any way splash/break the water's surface then it accelerates escape of the gases that you've worked so hard to dissolve into solution.



			
				bjorn said:
			
		

> ...And how do you know so much?  Seems you know everything from Chemistry to Biology in detail so well!!


Read, read, read and then read some more...   

Cheers,


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