putting the co2 hose into the tank with no diffusion will not achieve anything, the bubbles will simply rise to the top
do you have a powerhead lying around? if so connect the co2 tubing to the airline inlet of the powerhead if it has one, if it doesnt you can position the co2 tube under/inside the water intake of the powerhead so that the co2 gets sucked and crushed inside by the impeller
do you have a powerhead lying around? if so connect the co2 tubing to the airline inlet of the powerhead if it has one, if it doesnt you can position the co2 tube under/inside the water intake of the powerhead so that the co2 gets sucked and crushed inside by the impeller