CO2 Fluctuation in reactor chamber - Water height/Gas displacement

[AquaticJim]

Can anyone explain why the water height/gas displacement changes from one day to another sometimes in my external CO2 reactor?

My reactor is 20" tall and the majority of the time I will have only around 2" of gas at the top and 18" of water, but somedays the gas displacement will be as much as 10" inches.

Has this got something to do with the uptake of CO2 by the plant mass? It's not the waterflow being less/more on a given day causing itor a change in BPS, I know that much.

It's confusing me and I look forward to some suggestions/explanation as to why it happens.



This is one problem that I will need to eventually find a cure for. I have a bleed off valve that I turn and bleed the excess CO2 off each night just before the lights go out, but that of course necessitates me being here. The rest of the tank is pretty much automated, but I think there could be enough CO2 left in the chamber to cause problems with the fish. It's going to be a problem if I go away for a few days.

Thanks,

Jim

 

[Jim Miller]

Tell us more about how the system is plumbed, what filters are used, how water is moved to and from the tank.

Jim

 

[AquaticJim]

Here's a picture. The reactor is run off a Eheim 2217 -

 

[Jim Miller]

What controls the solenoid?

Jim

 

[AquaticJim]

What controls the solenoid?

Jim

The solenoid is connected through an electrical timer Jim.

 

[Jim Miller]

When this happens is there any ususual difference in your drop checker?

Perhaps the extra gas isn't CO2. Does this occur right after a water change? Another unusual event?

Jim

 

[AquaticJim]

No change in the drop checker.

It can happen after a water change and can also happen after a heavy prune of bunch plants. Thats why I was thinking it might be the plant biomass using less CO2, but I can't get my head around why that would cause the CO2 in the reaction chamber to be less willing to go into solution.

Maybe the water out of my tap is supersaturated with CO2?

 

[Jim Miller]

I wonder if it's just a bunch of bubbles sucked in by the filter intake from the "bleeding plants" or the gassy water coming in the with change and collecting in the chamber. See if you can correlate.

My tap water is definitely "gassy."

jim

 

[Left C]

... This is one problem that I will need to eventually find a cure for. I have a bleed off valve that I turn and bleed the excess CO2 off each night just before the lights go out, but that of course necessitates me being here. ...

Hi Jim

You could connect some tubing from the bleed off valve to the intake of an internal powerhead. The excess gas buildup would pass past the powerhead's impeller and get chewed up and then expelled out of the powerhead's output into the aquarium. You could leave it turned on 24/7 and you wouldn't have to worry about it or be there for it to operate.

 

[Tom Barr]

See the dual venturi DIY in the articles section.

This is a common issue as the day progresses in all Reactor chambers.

 

[scottward]

Can anyone explain why the water height/gas displacement changes from one day to another sometimes in my external CO2 reactor?

I think Jim is asking "why the water height/gas displacement changes from one day to another" not "why is there a build up".

So he is asking about the change in build up.

I have noticed this myself with my external reactor - and I believe the answer is a very simple one - ambient temperature!

A cool day there is less build up.

A warmer day there is more build up.

I'm pretty sure it's as simple as that - my observations have led me to believe this anyway.

But I am so confussed by this hobby that I have lost a lot of faith in what I know.

BTW - leaving the bleed valve open and connecting a line to a powerhead in the tank - in my experience with this (with my AM1000) - I think this ends up just bypassing the reactor too much. Could be just my particular set up, dunno, but that's what I've observed for what it's worth.

Dual Venturi CO2 works great if there is not too much build up (again, based on my experience/setup only), but you can risk dry running your pump if too much CO2 finds it's way into the impellor chamber.

Jim - one of my headaches at the moment - that gas build up in the top of your reactor - try turning your eheim 2217 off when the reactor is half full of gas - does this gas find it's way into the impellor chamber of the Eheim? Turn the power back on...is your Eheim dry running?

Sorry to give you a reason to worry - but if you are going away on holiday and you have even a very brief power black out - you could come home to find a burnt out pump.

It happened to me. :-(

I have a large swing check valve that I might fit between my pump and my CO2 reactor, haven't got around to fitting it yet, maybe the better solution is for me to get rid of that air gap instead, but I think the only way I could do this is by reducing the CO2 going into the reactor/boosting the water flow through it...

Scott.

 

[scottward]

Jim - any further thoughts on this one?

BTW - I believe the gas build up at the top of the reactor is O2 (not CO2).

 

[AquaticJim]

No Scott it still has me stumped mate. Just wondering how the build up could be O2? I don't understand how it could be O2?

When the CO2 solenoid switches the gas off it slowly dissolves and after an hour or more it's just straight water going through the reactor until the solenoid switches the CO2 on again the next day. If it was O2 build up it would always be there wouldn't it?

 

[Jim Miller]

Theory: CO2 with lights on causes pearling producing O2 which makes it way to the reactor and builds up there.

No idea how to test theory...without killing all the plants...

jim

 

[AquaticJim]

Theory: CO2 with lights on causes pearling producing O2 which makes it way to the reactor and builds up there.

No idea how to test theory...without killing all the plants...

jim

No I don't agree. My CO2 goes off 3 hours before lights go off (due to the CO2 build up in the chamber) and then the excess CO2 dissolves over that 3 hours.

If I bleed off all the CO2 to test the O2 theory, in that 3 hour period of the CO2 being turned off, reactor completely empty of gas, plants pearling like crazy......no gas build up happens in the chamber.


From my experience the gas build up in my reactor is pure CO2.

 

[scottward]

Irrespective of what the gas actually is, I'm pretty sure that the root cause of the fluctuation in amount of gas is due to ambient temperature. Just wondering if you have noticed any pattern there?

Based on what I have learnt, mainly on here, CO2 dissolves very easily whereas O2 does not dissolve so easily.

As Jim mentioned, whilst the plants are actively photosynthesising, the O2 levels in the tank will (should if setup allows), saturate. Due to the agitation inside the reactor the difficult to dissolve O2 builds up.

I'm pretty sure that the first 7-8 hours of the photoperiod are where the plants are the most active. The later part of the photoperiod the plants have 'had their fill' and slow down (and correspondingly their O2 production drops, therefore correspondingly DO levels drop).

So it's quite possible that in that last 3 hours where you are finding no further build up the reactor that this is because the water is no longer saturated with O2.

Could you conduct a simple experiment? How about off gasing the build up into an inverted glass? Then, put a lit match inside the inverted gas. If I remember high school science, the match will go out immediately if it's CO2, but will burn vigourously if it's O2....is this a crappy experiment or would it indeed prove what exactly the gas is?

I'm pretty sure that it is O2. I don't believe it could be a mixture of CO2 and O2, since I think the CO2 dissolves well enough.

In another thread I have asked for some further detail about CO2 solubility, with particular reference to the 0-30ppm band that we are interested in.

A well respected guru chiming in right now would be helpful.....

I have 'guru' status because I ask a lot of questions, not because I have a lot of answers.

Of all my hobbies, and I have many, this particular hobby is easily the most bloody confussing of the lot!

Scott.

 

[AquaticJim]

Don't know how 'scientific' this is, but I just did this a few minutes ago -

I have an oxy bottle for welding and I found a disposable plastic cigarette lighter in a draw. If I ignite the lighter and blow O2 across the flame it pretty much stays the same, maybe a slight colour change to the flame. If I blow the gas from the build up in my reactor across the ignited cigarette lighter (at roughly the same velocity as the O2) the flame is immediately extinguished leading me to believe that the build up in the reactor is pure CO2.

 

[scottward]

Very interesting.

I thought about this some more after my last post and I suppose their is a possiblity that it could be either CO2, O2 or both.

An extreme example would be cracking open the CO2 needle valve such that the reactor is 'hammered' with CO2. No doubt about it, in this scenario the reactor build up at the top is CO2 - the water flow cannot 'cope'.

On the other hand, I believe it is quite possible that the build up could be exclusively O2 after some time, for the reasons I posted above.

And of course, it could be a combination of both at varying ratios.

Gotta love this hobby!

I have no idea about O2:CO2 ratios with respect to extinguishing a flame. Your simple experiment seems like pretty good evidence to me that the majority (?) of the gas is CO2. Perhaps try this experiment right at the end of the photo period when the gas build up is at it's maximum to see what sort of result you get.

Question for the top gurus: If it were an O2:CO2 blend, would I be correct in thinking that the less dense CO2 would 'stratify' above the more dense O2? Therefore, even a very small amount of CO2 gas would be in the top most layer and hence that might be what Jim is bleeding off?

CO2 goes up to the ozone layer right? O2 stays down low - it is always easier to breath down low right?

Jim - if it's not to much trouble could you repeat the experiment over and over again until all of the gas is bled off? It would be interesting if the first few attempts continue to extinguish the flame but the lower portion of the gas mix doesn't.

This is an excellent thread that you have created Jim, I'm sure many others will chime in as they finish work/wake up........

(In other words, take what I say with many pinches of salt).

Scott.

 

[AquaticJim]

Jim - if it's not to much trouble could you repeat the experiment over and over again until all of the gas is bled off? It would be interesting if the first few attempts continue to extinguish the flame but the lower portion of the gas mix doesn't.

Done this about 20x now and the results have always been the same - flame extinguished.

 

[Tom Barr]

Jim - any further thoughts on this one?

BTW - I believe the gas build up at the top of the reactor is O2 (not CO2).

A simple test would be a flame added to the O2, it'll burn brighter/more etc, if.....it's pure O2.

The other thing, there's just more gas than saturation can handle....which is fine if........there's no turbulence and crashing down of the water on the media inside a reactor, much like a wet/dry............but the CO2 reactor is a very limited space.........so you see much more of it.

The bioballs degas the gases in solution, which get above 100% during the day.
Now most of this goes back into solution..........but some build up occurs.
O2? Maybe, it's tough to dissolve, CO2 is easy to dissolve though.

I do not think N2 or other gases build up....CO2 maybe some, but it tends to dissolve pretty fast even if the tank is 10X ambient ppm of CO2.........
I run a venturi line to suck out the gas once it gets to a certain point, this adds mist and then the gas bubble is regulated at a pre set level.

I no longer use reactors and if I do, I'd use a dual venturi design, one line comign from the CO2 gas tank into the needle wheel that goes to a reactor, and then a 3-4 cm deep air line at the top of the reactor which also has a line that runs to the same needle wheel. So as gas builds up to 3-4 cm, it'll start recirculating back into the chopper of the needle wheel.

This works quite well.