I own the mid size version. I am finding that over time, maybe a week or so, that the force of the pump is pushing the media upwards and in turn dislodging the lid causing the media to flow out into the sump. This has happened three times now. The first time I thought ‘user error’ . The second time I made sure all connections were tight, filled with a lower amount of media in both compartments and the same happened. Media spilled into the sump and was pushed around the tank.
I tried again this week and just used one media and removed the divider. The same has happened again. I can imagine this could be possible over time if the media/sponges get clogged but not in such short spaces of time in a cycling system.
I can only think that this unit has a design issue and is not fit for purpose. I have contacted Nyos and they have sent some replacement O rings so we will see
One more try!.....