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.