Brown typically means poor CO2. The dropchecker should be lime green when lights go on so if they are dark green when lights go on you'll need to either turn the gas on earlier or increase the injection rate. Be careful that you do not gas the fish. Make small adjustments and be patient.
Correct me if I'm wrong but the Eheim Pro 3 2073 is rated at 1050LPH or 263 GPH(US) so you're a little below optimal flow rating of 330GPH but it should still be fine, you'll just need to up the injection rate.