I mentioned this in another thread recently, thought it might be of interest.
I decided awhile back to add DIY CO2 to my 29 gal tank and quit using Excel. (I already had pressurized CO2 on my 90 gal.)
I built a 2-bottle rig with a gas separator bottle and diffused the gas thru limewood, letting the bubbles get sucked into the intake strainer of a Fluval 205.
The result was horribly inconsistent. The next morning, my drop checker was bright yellow! A day later, it was bluish-green, and the day after that it was solid blue.
So I sez to myself ... self, we need a way to even out the gas delivery
here. I had some pieces-parts on hand from when I first started using pressurized CO2 on the big tank, so I rummaged around. I found an old needle valve, bubble counter and reactor. I picked up a handful of cheapo check valves at the LFS and got to work. The resulting setup is shown here:
This setup gives me a pretty consistent 2-3 bps through the week
. I change out one CO2 generator bottle per week. My drop checker stays green all week. (I do give the bottles a swirl or two during the week and tweak the needle valve a little to keep it in the 2-3bps range.)
A consequence of restricting the gas flow with a needle valve is that you build up pressure on the generation side.
I worried at first about an explosion, but after playing around with my yeast recipe, I seem to have reached a "happy place". It's been running about 6 weeks now, no explosions.
Part of achieving success here might lie in the size of the gas separator bottle. You want it big enough to hold plenty of gas, but small enough to maintain/deliver good pressure to the needle valve. I started with a 12oz soda bottle, but have switched to a 20oz bottle.
Go to the grocery store and fondle some of the 2-liter bottles of soda. Squeeze them, you'll find they're hard as a rock. Now (presuming you haven't been arrested for fondling soda bottles) go home and squeeze your CO2 generator bottles and your gas separator. How do they compare? They might be fine or you might want to bleed some pressure off the system and re-think your yeast recipe.
If you decide to try this, remember to keep a close eye on it until you're comfortable with the setup - your mileage may vary. If it explodes and splatters sugar-water, yeast and ethanol all over your shiny new plasma TV, well ... I hate to say I told you so.
You could rig up a pressure relief system. I've seen descriptions on the net for various DIY pop-off pressure relief thingies. Rex Grigg sells a low pressure regulator that I think could work in this application. I'd put it between the gas separator bottle and the needle valve, so it can't get clogged by stray yeast-goo.
There's nothing special about my yeast recipe. Two cups sugar into a clean bottle, add boiling water to just below the curve. Shake, let cool to about 100F. Activate 3/4 tsp baker's yeast, add to the bottle. Mix and hook it up to the system. Good pressure in the bottle in about 2 or 3 hours, lasts me 2 weeks.
The check valves on the generator bottles allow me to remove a bottle without de-pressurizing the system.
In this system, leaks are a killer. I built my soda bottle caps using pieces of the Clippard tubing that Rex sells - it's a very snug fit in a 3/16" hole, no leaks.
to see the needle valve I'm using.
to see the reactor I'm using.