Trickle filter same as wet-dry?

Is a trickle filter the same as a wet-dry filter? For those that use CO2
injection also, do you experience a significant loss of CO2? How do you
minimize this loss? 

I use a wet-dry filter and CO2 addition. I maintained the pH at 6.8 before
the wet-dry. Now, with the wet-dry, the pH stabilizes at 7.3. The alkalinity
of the tap water is 100 ppm CaCO3 equivalent and the pH is 8.1. I decrease
the alkalinity using RO water to approx 50 ppm.

I'd like to reduce the pH to 6.8. Should I decrease the alkalinity further
with RO water (at the risk of pH instability)? If I'm losing CO2 at the
wet-dry, would it do much good to increase the CO2 flow rate?

Thanks for your attention and interest.

Shiao Y. Wang
Univ. of Southern Mississippi
sywang at whale_st.usm.edu