FishProfiles.com Message Forums

Seeing as how the logs was an innapropriate place to discuss the variable methods of CO2 diffusion, I thought that we should start a thread were we can discuss and analyze the different methods.

The discussion regarded whether CO2 should be added on the external or internal side of a filter

"Megil is correct when he uses "tech speak""


PLEASE EXCUSE THE PAINT DIAGRAMS
Frank does make some excellent points. While CO2 does displace oxygen and vice versa it is dependen on temperature and surface agitation as to how much of which is displaced. so having cooler temps and little or nor surface agitation it is ossible to make water rich in both O2 and CO2. Also even under 30ppm there is plenty of oxygen in the water, so it would be very hard to find true anaerobes in the filter since they would die in the presence of oxygen. there are many microbes that can switch between anaerobic and aerobic respiration depending on the environment, so I am assuming what frank meant as in a 'population' shift from aerobic to anaerobic bacteria is not so much a population switch as much as bacteria switching their method of respiration to adequately deal with a decrease/increase in oxygen concentration.

As for putting the reactor on the input side vs/ the output side is more of an efficiency issue more than it is a biological or mechanical considerations. Here are the mechanics of the reactor

CO2 gas is much less dense than water so it will rise up a water column. by placing the reactor on the input side, you have water moving from top to bottom, and CO2 bubbles going from bottom to top. Since there is a difference in diameter between the reactor and the tubing there is a difference in force. In the tubing the water molecules are tightly packed and moving at a higher speed applying more pressure on the space around it. Upon entering the reactor the water remains in high pressure for a moment before the water molecules disperse to fill the reactors volume, during the process they also slow down. the pressure in the reactor is less than the pressure in the tubing.

RED=HIGH PRESSURE GREEN/BLUE=LOW PRESSURE

CO2 gas being less dense than water will rise up the water column by the path of least resistance. with the reactor on the output end the water is likewise moving from bottom to top so the gas bubbles will very easily move up with the water, into the tubing and into the tank, decreasing the amount of contact time with the water.

When the reactor is on the input tubing- a counter current system is created that increases the overall contact time with water. On top of this the gas is exposed to water that is CO2 defficient so the gas more readily diffuses into the water. Very little CO2 diffuses out of the water into the gas bubbles.


Also if the pressure is strong enough the gas can be forced back down into the water. so the gas is forced back down into the reactor unable to escape to chamber until it is entirely dissolved.

Where red arrows indicate the direction of the water movement, and the blue arrows indicate the direction of the CO2 gas bubbles.[/font][/font][/font]

Hi,
We are apparently discussing different style reactors.
The reactor that I'm using consists of a cylinder with
an open space at the input end where gas and water mix.
The body of the reactor consists of several dozen small
passages through which the water circulates and then
exits into another mixing chamber and then exhausts out
into the tank. All the gas is retained within the reactor
and if any gas bubbles escape from this reactor, then
you have over powered the reactor or over loaded it with
CO2 gas.

Your regulator should have come with something that said
that stated the recommended rate of flow or the appropriate
pump to use. The physics is fine, provided your rate of
flow is enough to power the reactor optimally. Too little
and the gas will collect and move against the suction to a
high spot in the hose and collect. To great a pressure and
the bubbles will be sucked into the encased filter and pump
assembly.

In the end, I prefer the output for my reasons stated, and
if your system works and causes no problems,then I'd
continue to use it.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Frank can you provide a diagram of this reactor?

Hi Megil,
I can try. I can't even draw a straight line with a
ruler! Give me some time and I'll PM you.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Simply adding a inlet angle elbow will spiral the diffusion of the gas rather than blasting straight down.

Also, adding a venturi loop to a reactor will improve the efficiency.

Regards,
Tom Barr