CO2 Bubble behaviour

[Jonesy]

Hi Everyone,

Here's my story:
I recently bought a CO2 bubbler for my heavily planted 20 gallon tank (it wasn't that expensive and I've wanted to try one out for a while to see if they do anything). Basically this thing uses fermentation to create CO2 bubbles that are released into a diffuser (something that slows the bubbles progress to the surface) in the tank.

The Weird Thing IS:
I've noticed that the CO2 bubbles get smaller and smaller as they approach the surface... some don't even make it to the top?? I've taken some suba diving lessons and that doesn't really seem right....... shouldn't the bubbles actually be getting bigger as they approach the suface.... as the water pressure on them goes down??:confused:

Does this mean the CO2 is getting absorbed into the tank water... and this setup is working?? In the 2 weeks I've been using this thing I haven't noticed a difference in my plants (but it really hasn't been long enough to tell is it's working yet). Anyway, if someone can tell me what's going on I'd love to hear about it!!

[anonapersona]

The Co2 is getting absorbed into the water.

Sounds like the Hagen (Nutrfin) system. I like that for small tanks. I have 3.

A quick review of geometry will tell you that volume varies with diameter cubed. So if the bubble is reduced to 25% of the original diameter, the volume is reduced to (.25)^3 or 1.4% of the original volume. So you are seeing absorption better than that.

Next, be sure that you have sufficient lighting. Near 2.0 watts per gallon is good beginning point.

[125gJoe]

I was just wondering if you have any water flow on the CO2 bubbles to help disperse them? I've seen some tanks with a powerhead scattering the bubbles...

[djlen]

I've found that if I position my reactor as low as possible in the tank, the CO2 bubbles will be caught in the current coming from my cannister spray bar which will keep them from getting to the surface until totally dissolved into the water column.
They come out of the reactor as mist anyway, but the extra time in the water caused by the return flow really finishes the job.

Len

[anonapersona]

The Hagen/Nutrafin diffuser will have less bubbles if you push it down lower in the tank. The pressure of the water column will be a bit greater so the pressure in the reactor will need to be a bit more. I have no idea if the couple of inches of water's worth of added pressure willmake any meaningful difference, but I have observed the bubble rate slowing as the unit is moved deeper, and rising if it is higher in the tank.

I have mine just below the surface. The travel path of the diffuser is about 60 inches (24 ramps x 2.5 inches each) so an additional inch or two shouldn't be that important, especially if that makes a greater pressure for the yeast to overcome.

[Jonesy]

Thanks for the replies...... it appears my bubble mystery is solved!!!

I still find it surprising that the CO2 bubbles get absorbed so easily (they seem quite big) but it does make sense...... My diffuser is at the bottom of the tank and I do have alot of water movement through the tank. I'm trying to keep the surface agitation to a minimum (and keep some of this CO2) so I'm using 3 weak hang-on-the-back filters attached to an undergravel for filtration. If everything goes well I may be buying a few more of these things since I have a bunch of small tanks and would love to get more into plants....... I've been keeping fish for years and seem to have that nailed but I'm always struggling with plants (except for Java Fern.... which seems hard to kill)

Thanks again!!

[djlen]

HOB's generally are not conducive to good CO2 absorption due to their design which releases water back into the tank at the surface and creates surface agitation.
You might want to consider either external or internal cannister filters which move a lot of water, but can be adjusted so that the water movement is way below the surface.

Len

[Jonesy]

I have a piece of plastic blocking the outflow for these filters... so it reduces the surface agitation somewhat..... but there's PLENTY of surface agitation inside the filters and I'm probably losing CO2 (faster) there. I might try the internal cannister idea since I have a small one already.... and the bioload is very low in this tank. I would have to ditch the UGF but the plants probably like that better anyway?? (I prefer vacuming gravel to cleaning "CRAP" out of filters so I use UGFs as a pre-filter for almost all my filters... it has reduced my maintenance!!)