It looks like you basically purchased an expensive DIY system. Those commercial systems just put it in a nicer, neater package. Honestly though, you would have better results and it'd be a whole lot cheaper if you just mix your own recipe with sugar, water and yeast.
In any case, the rate of your CO2 is not that great. I have a 10 gal. running a DIY yeast system with a hagen ladder. My bubbles run about 1 every 1-2 seconds. When my yeast mixture is at the end of its life (about 2 weeks after mixing), I get about 1 bubble every 10-15 seconds.
The tube should be at the lowest possible point in order to allow for the highest amount of CO2 to dissolve into the water. This is better for the plants. Depending on your fish, you may need to run an airstone or powerhead at night to oxygenate the water. This will also add more O2 to the water for your plants at night, as plants take in O2 at night.
During the day though, there should be very little if zero disturbance of the surface. The water should flow around, but the surface should not be breaking. Doing so is only releasing the CO2 that you worked so hard to put into the water.
If leaves were falling off your plants before, it is unlikely that the problem was CO2, unless the plants you chose are heavily reliant on CO2. Your problem probably lies in your lighting and ferts. I would fix that problem before going further with the CO2 as you might not even need CO2 if you are doing low light. If you're doing high light and your plant's leaves are falling off, there is a bigger problem there than CO2.
I have a 10 gal with DIY CO2. I have a 40W 10K/actinic bulb, which essentially means i get 20W of useful light over my tank. That's not much, so my tank would be considered low light. I don't really need to add CO2, but I did anyway and it seems to have improved my plants growth, but I also started adding ferts at the same time I added CO2, so I'm not 100% sure it was the CO2 or the ferts that improved the growth. In any case, if you really want to keep the CO2, I suggest doing a DIY yeast mixture. Your tubing should be at the lowest point and run an airstone or powerhead at night to break the water surface only if you notice your fish are gasping for air.