Will this product provide chemical, biological, and mechanical filtration?

Yes. Power filters will combine the mechanical and chemical media into a single cartridge. The exterior of the cartridge provides mechanical filtration, while the media inside provides chemical filtration. Beneficial bacteria will also colonize on the filter cartridge, providing biological filtration. If you have additional questions please feel free to contact us at 800.545.1344. Thank you for your question. Customer Care Team

So when you replace the filter cartridge with a brand new cartridge you lose most of the established bacteria colony?

Thank you for your question. When you replace a soiled filter cartridge, biological filtration will start up again on the cartridge but the established beneficial bacteria living on aquarium gravel, ornaments, plants, and walls of the fish tank will remain, unaffected. The new filter cartridge will quickly remove organic pollutants and debris, keeping the crystal clear and fish healthy. If you have additional questions please feel free to contact us at 800.545.1344, we are here to provide assistance. Customer Care Team

what's actual size of the filter?

This is for Koller filters KC10 that uses small filter cartridge size and dimensions are 2.25 L x .5 W x 5 H Inches as per the manufacturer's specifications.