Our family about 3 years ago took down a pool and decided to build a pond after a lot of discussion we built a pond a little bigger then we originally planned about 6,000 gallons. We did some research and setup a skimmer filter and a waterfall filter. 2 years ago we added a UV light and a shed to hold the light and pump. Late last year before we closes it for the year the waterfall pump that is external would slow down.we were not sure why. This year as we are opening it the same problem seems to be happening. At first we thought we had a clog in the bottom drain possibly. Now we are seeing a small leak near our bulkhead to our bottom drain. We believe now we are getting air into the system that is causing the pump to slow. I will attach a few pics and I am looking for any advice. We are thinking of taking some water out and taking apart the bulkhead. Also we are looking to possible add a pre-filter of some sort and possible a sand or bead filter.