The bio media volume in that drawing is only 12ltrs. so this is why I put the heater separately as i thought i may be needing to add more sections for more media.
The fry grow out space is not necessary so i can add more media along the entire sump.
The whole sump is 900mm long, 300mm wide & 385mm high
Filter bag section,100mm wide
each bio filter section, 100mm wide
heater section, 620mm long (jager heater is 500mm)
return pump section, 180mm wide
so leaves me with 520mm of space