It is normal for the injector to spit out a bubble every few seconds. Keep an eye on that rate and when it starts to drop, either the injector is clogged (happens occasionally) or your
CO2 mix needs to be replaced.
I don't know anything about the accuracy of those
CO2 indicators.... and I'd be inclined to not believe them. However, if you are injecting
CO2 both the biowheel and the airstone are getting rid of the
CO2 as fast as you are injecting it. It would remove both, or at least only run the airstone at night. As far as removing the biowheel, your plants are giving you nearly all the biological filtration you need, provided the tank is at least moderately planted.