If you had a meter you would understand how little opening windows does, and for how long. The meter also shows you the trends and more importantly the peaks because that is where the real CO2 enters your system. CO2 is quick to uptake and slow to exit. That is why it is important to have a constant low number. What you are doing is analagous to dosing for calcium without ever testing it. While this may seem to work, in the long run you will not have the information that you need to properly evaluate and work with the levels that you are adding to your tank.
As to CO2 scrubbers, if you are battling a 2800ppm (or even down to the 1500ppm range) ambient CO2 level you are very unlikely to get anywhere with a scrubber. It is simply a mountain that the scrubber can not overcome.
My thought is that meters are cheap and they give a ton of information on the incredibly poorly understood role of CO2 in gas exchange that takes place in our aquariums.
As with all things it is your tank.