There are two problems with this:
1. Your more lily to kill your fish and fish provide co2 anyway.
2. When the pressure inside gets to big to escape through the airline its going to explode. It will through bits of plastic, sugar water, alchohal, and live yeast everywhere.

help plants and kill the fish.

ive tried this and it didnt work suggestions

 It's not a reaction, yeast is alive, and basically once it eats the sugar, it farts out CO2. =D

"...and they get very happy."

You can speed up the reaction by warming the water up a little before. Yeast grows the fastest at about 95 degrees Fahrenheit. Be careful not to make it too hot though cuz you can kill the yeast. BTW the reaction is fermentation. The yeast is turning the sugar and water into alcohol.

Instead of / or to use with the check valve, I use a second bottle for the gas to pass through first to act as an overfull catch can. Helps to stop any mess getting into the tank

Oh..its not called a diffuser, its a reactor...my bad...

Hey .. LIke the video..I was reading on another site about these C02 rigs..they suggested some sort of diffuser at the aquarium end of the tube so that the C02 doesn't just go up in bubbles ..it forces the C02 to be absorbed into the water..they used a small aquarium vacuum...? I dunno, maybe something to check into?

can you come up with a home made automatic fish feeder next, possibly containing enought food to last around a month

I noticed that you ran your aerator during the day. I would recommend that you only run it at night, because during the day the plants will make enough O2 (oxygen) to offset the CO2 (carbon dioxide) so you don't need to use an aerator. But at night you do need to run it because plants take in O2 instead of CO2. So at night if you are not careful you could end up with excess CO2 and some major pH swings.

Sweet! I am so making a dozen of these. (One for my aquariam and the rest to give my enviro-freak friends a coronary when they come over >:D )