You need a way to disperse the bubbles throughout the tank before they reach the surface. You can position the diffuser under the outflow of your filter, or some people put in under the intake so the Co2 goes through the filter...depends on your setup. Another easy way is to use a powerhead and blow the bubbles all over the tank.
I assume you are using a ceramic in tank diffuser . If so, I don't think you will ever get 100% diffusion. You will need an inline diffuser. More specifically an inline co2 reactor.
I have an atomic inline co2 diffuser that's connected to my canister intake. As the water gets sucked into the canister it also takes in the micro bubble from the atomic diffuser and theoretical it is supposed to achieve 100% diffusion so there are no bubble coming out of the output but I still get some bubbles. I think for 100% diffusion you need a reactor. I see a lot of people talking about rex rigg reactors but I've never really looked into it too much.
Yes a large amount is still dissolved. I simply airstoned my co2 from pressurized tank and got all the desired effects. Sure some was wasted. Co2 has a very high affinity for going into solution even from passive bubbling, but as mentioned efficiency boosting methods are out there.
If you want a better dissolution method it can be bought. If not, turn up the co2 as is and use your testing to get the same ends anyway. I was still getting three months per cylinder even off wasteful airstone use.
GLA has some Atomic diffusers that are pretty good. Also, I have an old Red Sea reactor that is good for 2-3 BBS, but no more. My Crypts pearl with it. I know that I am far from 100% dissolution, but still, efficient enough .
I tried a reactor for a while and ended up with an in-line diffuser on the intake of my external pump. I found that resulted in the smallest micro bubbles and the best circulation around the tank. I don't see any bubbles getting to the surface. In addition I keep my tank lidded to trap the out gassed CO2 under the lid in order to slow down the out gassing and allow me to have surface agitation without much loss of CO2. This allows me to saturate my tank to fairly high CO2 levels while maintaining a flow rate of about 1 & 1/2 bubbles per second.
You should check out the ISTA max mix inline reactor, cheap and easy to use. I started with an inline diffuser but got frustrated with how quickly it gunked up so I switched to the reactor. As mentioned lots of people make reactors themselves but I am not much of a DIY guy.