Algae will grow on the diffuser, just like anywhere else. You'll have to balance the CO2 with your fertilizing and lighting before you can really get a good handle on it, usually. Or at least that's the case in higher light tanks. And all the little CO2 bubbles won't completely dissolve in your tank water, that's normal.
Do you have a drop checker on the tank, by any chance? If so, what color is it? And you can soak the diffuser in a bleach solution every now and again to get rid of the algae build up.
Do you have a drop checker on the tank, by any chance? If so, what color is it? And you can soak the diffuser in a bleach solution every now and again to get rid of the algae build up.