I am looking for a filter system for my small pond we installed in the backyard. We have one pond at 800 gallons and one pond at 300 gallons. A small stream 4 foot wide and 20 foot long connects the ponds. The stream and ponds are lined in rocks. The gutters from the house drain into the pond. At this time we have no filter installed, and a sump pump transfers water from one pond to the other. The elevation of the ponds is minimal. and flow is slow from one pond to the other. I want to install a filter system but do not know my best options. I would like an eternal inline filter if possible. Any suggestions would be appreciated.