I already have hydrophila japan.
I think this might be a better DIY setup. I got this one from Amazon here It has a Solenoid Valve and Bubble Counter. I hook the Solenoid to a timer set to stop an hour before my lights turn off for the day and come on about an hour before the lights come back on. Also here is a YouTube video of how to set it up using Citric acid and Baking soda.For a simple DIY CO2 solution (yeast, sugar, water), a few challenges come to mind: (1) The production rate of CO2 isn't always consistent; (2) It can be difficult to estimate how much more CO2 can be made before additional additives (yeast, sugar, water) are required; (3) Once the reaction is started, there is no way to temporarily halt it (say, at night) and "save" it for later use. You always need a release for the CO2 that is constantly being produced and stored in the bottle. If you don't have a release, a mess is inevitable. Turning off a commercial CO2 injector that uses a cartridge, cylinder or cannister is straightforward; (4) Fine tuning the flow of CO2 can be challenging using just an air diffuser; and, (5) quality of construction (e.g., drilling holes in bottle caps and properly sealing to prevent leaks).
Take a look at the video below, which is a much more sophisticated DIY CO2 setup that uses Citric Acid, baking soda & water.
HOW TO: DIY CO2 system for aquarium plants TUTORIAL