Just take the carbon out of your filter. I hardly use it all anymore, and never in my planted tank. The only use I have for it is to occasionally remove tannins from my non-planted tank. Water changes take care of the rest.
As for your CO2 indicator, what is it? The best way to measure your CO2 levels are to find out your KH and pH then check a CO2 chart. You should aim for 20-30 ppm, but not more than 40. If your current indicator says the CO2 is too high, but you don't have anything putting CO2 in the water, that sounds like a case for a faulty indicator.
I hope you didn't just buy the Carbo-Plus thingy. If you did, in my opinion, you wasted your money. Check out the thread on this page about an "electronic carbon dioxide" thing, as well as many others. Pressurized is better and cheaper in the long run.