Additions to the filter can be very useful a few ideas are

1. chemical treatments
1. Zeolites; place inside mesh bags will absorb chemicals from the water improving the water quality. The bag helps in removal of the zeolite for recharging in salt water
   • Water softener zeolite absorbs excess calcium and magnesium salts from the water this can be trouble, hard water buffers pH changes!
   • Ammonia Absorbant zeolite absorb ammonia and other nitrogen by products from the water that promote algea
   • Phosphate absorbing zeolites absorb phosphates from the water that promote algea
2. Activated Charcoal; placed inside mesh bags will absorb all chemicals in the water including medicines and organic wastes and discoloring in the water, so remove any activated charcoal before medicating the pond!
3. Calcium Carbonate; such as crushed coral will keep the water hard, which helps a lot with pH buffering
4. Flocculents; cause suspended solids to either fall out to the bottom of the water, or float to the top to be skimmed off. I've had very good results with Accurell F, But its hard for me to find now
5. chemicals to bind ammonia, chorine, and chloramine are readily available
2. aeration
1. Mechanical Aerators; are available which can force a great deal of oxygen into the water
3. physical treatments
1. polishing filters; very fine mechanical filters can remove extremely small particles leaving the water crystal clear, the are rather expensive and require a lot of maintenance.
2. Protein Skimmers; devices that use oxygen to cause proteins and organic wastes in the water to foam up similar to beaten egg whites (not as thick) a lowing the foam to be removed. Use extensively in salt water aquariums
4. sterilization treatments
1. Ultraviolet Lights; properly sized and at the correct flow rates will kill all of the floating algae and bacteria in the water. They also greatly reduced other parasites that can effect your fishes health.
2. Ozone Treatment; ozone kills the algae and parasites in the water passing through the treatment device. The ozone has to be removed from the water before it is returned to the pond or it will kill everything there too, I don't recommend it for casual use as its technically demanding
5. waterfalls and fountain heads no limits here, except that water lilies like still water