A few tips for correct pond management:

• A pond biological UVC filter is actually a sewage treatment plant for your pond. It should not be considered a vacuum cleaner.
• This vessel must work dirty, but be porous. It should only ever have clear, solids-free as possible, potentially toxic water pass through it for treatment by the UVC light and the beneficial bacteria living within the vessel.
• Do not wash out a biofilter because you think it is dirty. Pond foams & media must only be washed in non-chlorinated water (say pond water) & only when choked. The pump must be switched back on within a few hours to prevent major loss of the bacteria from oxygen starvation.
• The pump should be mounted well off the pond floor to reduce the solids intake and also to allow higher oxygenated water to be pumped through the biological system. Oxygen means healthier beneficial bacteria. The water on the floor of the pond contains much lower levels of oxygen.
• Removing debris from the pond is a separate issue. When removing debris from the pond, the pump must be switched off to prevent stirred-up mud from being drawn into the Bio-filter. This smothers the bacteria.

Manage your pond as above. Keep the fish to low stock levels. The pond will be a pleasure & low maintenance.