Yes, your internal filter can be positioned horizontally, as long as it is fully submerged in water and the inlet section is not blocked or obstructed in any way.

However, please note that when positioned horizontally, it may not be possible to use certain components such as the venturi pipe or spray bar, as these will likely be submerged under the water and unable to function effectively.

Make sure the filter is properly positioned and the water intake is clear to ensure optimal performance.