25 l biofilter (non-pressurised) filter. Mechanical filtration via set of foam sponges easily rinsed by hand. Typically 35l/min flow rate and good for smaller ponds up to a maximum of 4,000l stocked at hobbyist levels of fish. Bio filters pond capacity is indicative only – if unsure always buy the next biggest version. You can never ‘over do’ biological filtration, and you never want to ‘under do’ it either. Includes bio balls.