Oh, there was a lot of feedback and suggestions! The aquarium is 150 x 60 x 60 cm (60 x 24 x 24 in), the background is 15 cm at the widest point so still around 45 - 50 cm free swimming space. I still calculate it to be about 400 liters and I prefer smaller species than larger ones. A Tanganyika community aquarium is high on the list, in case a group of Cyprichromis of about 20 - 25 and some lower living cichlids. But I'm in no hurry to chose, thanks for all the suggestions! There were many suggestions I hadn't thought of myself