Pressure generated by yeast-based DIY CO2 system?

[cgrabe]

Hey, I'm considering redesigning my 44ga. tall aquarium as a planted aquarium and am trying to decide what all I'm going to need. I'm drawing out a design for a DIY CO2 injection system based on the sugar/yeast concoction that seems to be pretty popular.

I would imagine that once the CO2 production gets up and going, the air-stone will act as a sort of regulator and maintain a relatively constant PSI inside the system. Does anyone have any idea around how high that pressure would be?

I ask because I would like to build an adjustable relief valve so that I can control the amount of CO2 being injected into the water. I'd like to know what scale I need to be thinking on. My thinking is that if I can reliably and predictably reduce the pressure behind the airstone, I'll reduce the amount of CO2 injected. Have any of you done something like this?

Perhaps I should instead use an adjustable low-pressure regulator in addition to the static relief valve to safely maintain a constant flow of CO2? The relief valve should be relatively easy to make, but I'm not sure how I'd go about making a simple regulator. I'll have to read up on that. Any comments are appreciated.

 

[beviking]

I think that's a great idea! You may want to find the psi rating on the container(cola bottle, juice bottle, etc...) that you will be brewing the yeast in first. Too many first hand accounts of capping the soda bottle tightly and then a big bang makes a big mess!
I don't believe the air stone restricts the pressure at all. One of the minor problems of yeast is getting steady flow. You may waste CO2 with a blow-off valve. I don't know for sure, never did DIY, only researched it.
Hopefully someone with experience will chime in.
I'm all for DIY!
Good luck!

 

[TonyN]

There's no way you are going to get too much Co2 from a DIY made with a coke bottle. I dont know why you would need a relief valve.
I've been running one for a few months now. I diffuse with a wooden air stone and my Co2 count and pH are very stable. After a couple weeks the pH starts to rise and I know its time to put a fresh mixture in.
I only have 20 gal., so I would think that in your 44, the problem would be getting enough Co2. I dont think you're going to want to reduce it with a relief valve.
Ok - now fess up. Admit it. You just want something to tinker around with. Cant blame you, I'm the same way

See Ya,

 

[cgrabe]

Originally posted by TonyN
Ok - now fess up. Admit it. You just want something to tinker around with. Cant blame you, I'm the same way

Ok, ya got me. I like building things. The only reason I wanted a relief valve was to save myself a lot of cleanup if the airstone got clogged or something. The way I understand it, the pressure would continue to build, however slowly, as long as the yeast was alive and had nutrition. That would likely never happen, but I'd hate to be proven wrong. As far as getting enough CO2, I was planning on at least two or three 2-liter bottles. I've been reconsidering though and may end up not doing any of it.

 

[TonyN]

Well, you should at least give it try. It doesnt cost much and I had a lot of fun fiddling around with mine. Trying different recipes and different diffusers and stuff.
And you know, as a side effect, it helps the plants

 

[cgrabe]

Maybe in a future tank. It looks like this time I'm going to put together a cobblestone bottom. I'm going to put a drain in the bottom with two tubes. One will lead to the filter input and the other will lead to a permanently placed syphon with a spigot for easy draining of dirty water. Waste should be pulled right into the drain without using one of those gravel vacuums, but if a bit gets left behind, I can vacuum once in a while. I'll probably include one or two terra cotta pots holding some java ferns or something. I think CO2 injection would be overkill in that setup.


(somebody stop me before I build my own tank out of discarded contact lenses :sad )

 

[TonyN]

Sounds way cool. You've got a lot more ambition than I do.

Good Luck,

 

[got_nailed]

As for the PSI. For every foot of depth you go down in the water it will equal a pound of presser. So if the air stone was 1 foot into the tank it would give you about 1 pound of presser in the line. I have found with out putting an O-ring in the top of the Coke bottle it is hard to get my DIY Co2 to work at a foot in the water.

Depending on how you seal your hose to the top of the bottle it will leak at a pound of presser.

 

[QCppg]

Coat the O-ring with vaseline or another food-grade petroleum jelly. It'll be gastight so you'll get more pressure from the system (I used vaseline to seal a faulty impellar housing on my Aquaclear 150).

As to recepies the yeast will utilize all the available sugar so long as it isn't enough to kill the mixture. You can also add more sugar once the yeast has used up all the available sugar. You can only do this so many times before the alcohol produced by the reaction kills the yeast. I think four to six ounces per gallon would be sufficient to start the reaction (mind you this proportion was taken from a beer recipe).

 

[got_nailed]

I dump ¾ of the water out. Put 2 cups of sugar back in, and fill with warm water. If you let the yeast die that you should start all over. The amount of Co2 will be determined by the amount of dissolved sugar in the water. If there it is low on yeast then it will tack a little longer to get going but as long as you have some health yeast going you’ll be fine.