The amount of Matala needed will vary with each pond and design. Some filters are too small for the pond, but you can improve filter performance with Matala. Some hobbyists may be open to upgrading their system to a larger filter size.
In general, we can shoot for these guidelines:
When deciding how many sheets of Matala are needed for your pond, think 1,2,3,4. This is the number of sheets per 1000 gals depending on your fish load. The fish load really determines the volume of any media required. Many hobbyists' filters are too small for the fish load. Your pond could still function reasonably well because ponds are very resilient and manage to adjust to high fish loads even with small filters. However, a pond with a high fish load and a small filter will need to increase maintenance and care. You will likely have bigger algae problems and fish health issues if your filter is too small.
Water Garden Ponds: Use the black or the green due to higher quantities of solid waste present. A true water garden has very few fish and the biological filtration is carried out by plants and algae in conjunction with the bacteria and micro organisms that attach to the extra surface provided for by plants and macro algae. The main focus of filtration would be solids removal.
Use approximately 1.6 cu. ft or 1 full sheets per 1000 gals. as a minimum. Of course high fish loads will necessitate additional pieces of the blue or the gray to increase biological filtration.
Ornamental Ponds with greater fish to plant ratio. Again use at least 2 to 3 cu. ft. or 2 full sheets per 1000 gals. The fish load rather than the water volume will determine the amount of Matala to use. As your fish population grows and increases in number you must provide at least double the Matala to give your fish the right conditions. This equates to 5 cu.ft. or 3 full sheets per 1000 gals..
Koi Ponds with no plants: Usually this is the type of pond where many high quality koi are kept and water quality is of utmost importance to maintain the health and growth of body required. Typically these ponds require larger filter systems, preferably with multiple chambers whereby solids are separated from the biological chamber. Matala can be used to full advantage in multi-chamber systems. All 4 densities can be used in series or combination to give desired results. Use 6+ cu.ft. per 1000 gals. or 4 full sheets to achieve excellent water conditions. This relates to a minimum filter size being 10% to 15% of the volume of the pond.
The Hobbyist's Dismay
Unfortunately, in this hobby, a lot of generalized misinformation is given and applied to many different types of ponds.
Hobbyists are told that 2 cu.ft of media will filter a 4000 gallon pond for instance.
Then reality hits and he finds that he really needs a much larger quantity. Many hobbyists have completely inadequate filter systems.