the stuff on the back wall looks like diatoms, as does the stuff coming off the filter outlet. otocinclus catfish will actually feast on it. diatoms will go away on their own as the bio filter matures. the only thing you can do for it is be patient. it takes a few weeks for the filter to mature enough for the diatoms to go away. and try not to add anything to the tank that will increase the bio load. except otos that is, since they will eat the diatoms