This is a huge debate among some. I'm on another board dedicated to plant enthusiasts and the general consensus there is, yes, you need pressurized CO2 for such an undertaking if you want real success. The key being "real" success. But if you don't also have adequate light and fertilizer you probably won't grow great plants either, are you doing those?
if its ''mostly'' anubias, what are the other plants? Anubias are slow growing and do just fine in low-mid light. Absolutely no Co2 is required...though when supplied with high light since they grow so slowly, algae may collect on the leaves without Co2 supplementation, and other faster growing plants to take nutrients out of the water column starving the algae.