Right... please tell us more about your pond. What are the dimensions (L x W x D)? What kind of pump are you running (external or submersible)? What is the flow rate of this pump at head? Does your pond have a main drain? Does your pond have a rock and gravel bottom? Tell us more about your DIY blue barrel filter.
Please understand that there are two unique system types out there. Koi pond are different than water gardens, and the equipment selection and configurations are different as well. FYI - Your Pondmaster 4000 is a water garden filter, and is woefully underated for use on koi ponds.
Kind Regards,
Bill