Im trying to make a diy c02 diffuser without having to add another power supply. My effforts have got me using a old gravel vac tube with tubing going thru a small cap on top of the gravel vac with a air diffuser on the end. My thoughts are that the c02 will come thru the small tubing and into the gravel vac, it wont get dispursed around the tank but it will be kept in the water for a long time thus dilluting eventually. This will be attached to 2x 2ltr sugar/yeast mixes on one side of my 75 gallon tank and i have another 2x 2ltr mixes attached to a powerhead.
Does this sound like it will work ?
That diffuser won't be very effective. There is no water flow through it, so the only way that CO2 gets from the inside to the outside of the tube is by diffusion out the open end. Fairly quickly the tube will fill with CO2 and begin to shed big bubbles of CO2 that quickly float to the top of the tank. You have to have water flow through the diffuser pipe for it to work.
If you build one like mine and place it level with your canister, and place it on the intake, you wont have any bubbles. The co2 comes in from the bottem an goes up while water comes in the top and hits the bubbles breakin them down untill they 100% diffuse then they pass into the canister to be distributed into the water column.