I finally bought a KH test kit by Hagen. Wohoo! The results showed 90ppm. That with my pH at 6.2 equals CO2 at ~56ppm.
Good thing I haven't added fish yet.
Most CO2 (pH vs. KH) charts I see have the usual pH units, but are the KH in german degrees? I used the 90ppm*(0.056°/ppm)=5.04°KH to get the reading in german degrees. Is this the correct conversion for alkalinity?
To reduce the efficiency of my CO2 diffuser, I turned up the flow rate of my canister filter. Full speed ahead! This helps to agitate the water surface a little more and causes some of the larger CO2 bubbles to float to the surface. Before the bubbles were trapped in the diffuser and could not escape until they were completely dissolved. I hate to waste CO2, but the system would probably work better on a 20-30 gallon aquarium.
The plants are sure loving it. I had to do some minor trimming last night and moved the larger A. crispus to the back.