Thank You, you are right I have the only one CO2 diffuser on the right side of the tank, two inflow and one outflow pipe on the left. The water in the tank create whirl and CO2 is distributted all over the tank (I used also drop checker to be sure). I use pH controler to have CO2 stable. Filter are two Eheims each of them has separete inflow pipe and are conected to one outflow. Teperature is 28° - 29°. Stones are dolomite (I have found them in Italy).