I was going to go with a pressurized CO2 system for my new 75g dirted/planted tank but decided to first increase my measly stock lighting by adding a double T-5 along with my stock lighting. Well that blew my budget for now so I started building my own DIY CO2 generator. Pic below is after the lighting upgrade, I still have a good bit of tannins in the water from the Mopani wood, it took about 6 months of weekly water changes to finally get the water clear up in my other 29g tank.
DIY CO2 in progress:
1] 25ft polyethylene 1/4" tubing (supposed to be CO2 proof, it's a little more ridged than vinyl but still flexible enough to use. This size fits very tightly on the brass barb. Tubing $3.00 for the roll
2] Brass barb, 1/4": $3.00
3] 2L soda bottle, free I guess as I drank the contents.
4] Plumbers "Goop": about $5 for a tube large enough to last me the next 10 years (if only it would keep that long).
I decided to get a 1/4 brass barb, heat it up and carefully push it through the 2L cap thinking this would make the tightest possible connection.
It took me 2 tries to get it hot enough to melt through the cap. I kept the soft inner plastic washer in the cap because I know that is what helps keep the seal on the soda bottle, I just melted through both of them.
I then pulled the barb back out, cooled it under water then dried it off very well.
I put a decent amount of plumbing "goop" on the inside of the cap, but not too much as I didn't want it to interfere with the threads. This created a really good seal on the inside between the cap and the brass barb. Then I carefully put some around the MIP end of the barb on the outside of the cap in a " ring" around it to make a top seal. I think the seal is pretty good because a very small amount was pushed through to the outside of the cap when I put the barb through the hole I melted.
So here's the final product:
I'm going to let this cure for at least 3 days to let the VOCs evap off. Regarding the use of plumber "Goop" I found a number of people online who had used this "because it is one of the few glues that will adhere to poly-E and poly-U which the cap is probably made of. I found no instance reported of any residual VOCs causing harm to any of their fish or plants.