Biological vs Mechanical Filtration
Filters are used to remove suspended particles from the water (mechanical) or they process the water biologically, removing nutrients and organic pollutants using bacteria. A mechanical filter is attached to the intake of a pump and is submerged in the pond. The filtration media is fine-pore polyester or extruded plastic material that traps the particle until it is removed by you and rinsed away with a garden hose. The biological filter uses the same material but is located outside of the pond where the water is pushed into the filter rather than pulled through it. The water flows through the material which is full of beneficial bacteria which cleans pollution from the water. Ideally a biological filter would be pre-filtered with a mechancial filter (like the filters found in a skimmer) to keep the media as clean as possible to maintain peak efficiency.
To figure out how much water is in your water garden
Multiply the average pond length, width, and depth (all in feet) to get the cubic volume of the water.
Multiply by 7.5 to get the total gallons of water.
For an irregular shape, try to estimate the actual square footage as close as possible by dividing up the surface into smaller squares and circles that are easier to calculate.
Be sure the depth is average depth, not the just deepest point; measure in several places.
Average length X Average width X Average depth X 7.5 = gallons of water.
Another way to measure pond volume is to use a water gauge for the garden hose that can be purchased at a hardware store. Additionally, you can find the amount of time it takes to fill a five gallon bucket, then time the filling of the entire pond and divide the total number of minutes by the time it took to fill the bucket.
A floating filter means it needs to be cleaned.
It takes time for a bacterial colony to develop; wait four weeks before adding fish to a new pond.
When cleaning the filter media, rinse only enough to remove the silt and dirt. You don't want to rinse so thoroughly that you wash away bacteria.
Filter media must be replaced periodically. If it shrinks or deteriorates, replace with new.
If a filter clogs too quickly, try less dense material that allows more particles to pass through.
If the filter doesn't take out enough "green water", try using more dense material.
Polyester and plastic filter media don't clog as easily as less efficient filter material, like lava rock, or similar. Plus, it's much easier to clean and has way more surface area with which to grow beneficial bacteria!