Bottom weld is an extrusion weld that is significantly more powerful than a regular weld.
very small
Very huge volume for a bio carrier makes it ideal for ponds with a lot of fish (combi filters)
Control box mounting distance from the filter is up to 4m (longer cable lengths on request)
No drive shafts with seals below the water's surface, gear driven (prone to leak)
Swimming pond-friendly 24V drive system (25, 50, and 100 m3/hr models)
superior control box