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CO2 outgassing in cannister filters

Hari wrote:

>Karen and APD:  
>I was browsing through the archives where you said that a cannister
>filter would outgass more than, say, a biowheel setup. 

Either you mis read what I posted, or my fingers were more disorderly than
usual that day.  Properly set up, a canister filter will _not_ outgas more
CO2 than a biowheel... although Biowheels outgas less than you'd expect if
you keep the water level in the tank high enough.

> I have an Eheim
>setup with the spraybar underwater, aimed away from the surface of the
>water, which I thought would cause little to no outgassing compared to
>another setup.  Can water movement underneath the surface of the water
>(which is without ripples) cause significant outgassing?

Any water movement will increase surface turbulence to some extent (over
water with no movement at all) but water movement is important too.  In
water with no movement, the prandtl boundary makes it harder for plants to
take up nutrients including CO2.  So we have to compromise by trying to
have reasonable water movement BELOW the surface, while keeping the surface
as quiet as possible.  The way you've set up your Eheim is just fine.  

Karen Randall
Aquatic Gardeners Association