Penguin Bio-Wheel Compatability

Yes, the more surface agitation, the more air:water interface=quicker exchange of gases, all gases. It woud still be worthwhile to inject CO2 as long as you keep the surface disturbance to a minimum. Keeping the water level higher should do this. Once the CO2 is in the water, it goes wherever the water goes, including through the filter. With the bio-wheel, any water going over it will loose most if not all the extra CO2. So you'll be losing CO2, but as long as you keep injection up a little higher, it will still be beneficial.
It isn't the best choice for that application though.

Not in my fish tanks, thanks anyway. Biowheels are excellent biofilters, but the poorest choice of filter format for planted tanks.

I have a penguin biowheel 170, and I agree that the biowheel makes an excellent biomedium. But, I agree with RTR.. the biowheel is a poor choice for a planted aquarium. If I had the foresight, I would have waited to remove my bio-wheel from the filter until after I could get numbers for how much CO2 I have disolved, but I didn't. But, I can only keep 12-14 ppm of CO2 in my tank without the biowheel, so I don't think it would be a good idea. I also took a knife and removed the "lip" at the bottom of the discharge chute on the penguin also, to reduce the surface ripple it creates. (It now creates next to none, the water goes pretty much straight down.

Granted, I also have a tetra 30 in my tank also, in preparation to seed a new tank. (going to move the whole darn filter to the new tank when I get it.) So my numbers may go up some when I remove the tetra. I'll post and you know how much when I get the new tank. At this point, it may be a bit.. money isn't going to the places I wanted (namely, my bank account....) Story of my life lol!

If you have it, I'd use it, just without the bio-wheel.

I think the general consensus among people who keep planted aquariums is for canister filters. They make CO2 injection easier because they can be used as a CO2 diffuser or inline with one.