The red ball is floating at the top of the clear indicator vessel on top of the filter?

The filter needs cleaning.

1. To clean the filter turn the valve from RUN to CLEAN. Water will stop returning to the pond and instead leave by the drain on the rear of the filter lid.
2. Wind handle on filter to squeeze sponge inside and help remove dirt. Dirty water will then be pumped out of the drain to waste.
3. Turn the filter valve back to RUN, and normal filtration and return to pond will resume.
4. To access the sponges for inspection or replacement, slide clasp on clamp ring to the right, while at the same time depressing the left hand side of the clasp and pulling to the left. Use two hands.
5. Lift the lid and connected sponges out of the filter body and turn upside down.
6. Remove the bottom shield
7. Using a screwdriver (not supplied) undo the screws in the bottom support plate.
8. Sponges can then be lifted off and replaced
9. To clean black Bio Balls in the base of the filter, remove by hand and wash in old pond water, then replace.
10. Reverse steps 4 to 9 to ensure the clean Bio Balls and sponges are re-installed correctly and lid is closed.