Man it's been hard to find a sketch layout using 55 gallon barrels and what I think is called a retro-fit filtration system with pipe sizes leaving the pond going through the filter and out of the pump. I have this design using all 2" pvc but I'm not sure if I should use a larger pipe leaving the pool into the filter and if a smaller pipe might be better leavings the pump going to the pond? I'm really confused with the water level of the pool vs the barrels so i'm guessing when the pump is off the water level will be the same in all the barrels and pool. When I turn the pump on I'm guessing I will have about 1" drop in each barrel so buy the time the water hits the last barrel the water level might be 4" lower than the pool level?

Any guess if 2" pipe will work thought the system? I have to have a starting point and need to know if I should use a 1.5", 2" or 3" bulkhead at the pool? I have a 3500 GPH and 7000 GPH I can use or I could buy a different size if need be? I forgot to mention it covered and I'm going to have a netting over the pool as well so no leaves should go into the pool. I just hope no raccoon tries to climb in and tear up the liner.