Another thing you could try also is pack some carbon in the canisters to pull out more doc's out of the water. I did that for a month in the planted tank & the water became ultra clear & the plants did not mind.
I am guessing you run 24/7 with the CO2 because you have a controller? If not, I would not run at night because you are wasting gas & stressing fish. It could also contribute to the planaria problem , because there will be less 02 anyway during this period & higher CO2 is not going to help in my opinion. If anything, higher O2 would help rid Planaria even if it is not a direct cause. A tank with higher O2 levels is healthier within reason as long as it is not saturated. Increasing surface agitation could also be worth a try. Just a thought.