I suggest you read through this forum extensively to educate yourself on the nitrogen cycle, beneficial bacteria, how to properly clean a filter without killing off that beneficial bacteria, the need for plants in that cycle and much more.
You will read that a lot of us don't use store bought filters, instead we use a bog filter. The water gets pumped under 12 inches of pea gravel, rises up through the gravel and returns to the pond. Plants, which thrive on the excess nutrients, are grown directly in the gravel. The bog filter can be small or large. In your case it won't need to be very big since your pond is only 100 gallons. A wooden box with a liner or a long window planter would probably work for you. You won't be wasting money on an inadequate store bought filter and the bog will keep your water crystal clear with no maintenance. No cleaning of any filter pads at all.