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[goose22]

if the pictures would load up,says file to big? i have a interpet fish pod 120L, it has a push out piece on lid at right hand end, also a pice that corisponds, on the trip tray, to cut out, whats it for?

 

[Aquascaper]

Without pictures I can't be sure but sounds like removable pieces so you can add an external filter with pipework.