Just sharing my humble outdoor pond of which I hardly have time to take care of. Surprisingly though, the inhabitants flourish in there regardless of the lack of filtration. All I have in there is a 2.5hp water pump for constant water flow over some japmats for bio. Other than that, a bi monthly flush of 90% water change. I actually don't know how much water the pond holds, it is over 20 years old. The current stock is: 3 alligator gars which I introduced as 5" babies around two years ago. They are currently around 30-36", each tile is 6"x6" for reference and very thick. Actually as thick if not thicker than my forearm. I also have 3x channa micro peltes in there that are 20-24" that I put in as babies during the beginning of the year. I had a bigger trio in there last year but unfortunately those didn't make it when I placed them in a holding tub during the past winter. Somehow, jumped out of it(2 feet clearance). Last but not least, the oldest inhabitant is a 10+ year old red ear slider than has been in there. Here are some pictures I snapped up from the second level balcony. There was also a bunch of red belly piranhas around 5-6" that I put in there before but they all disappeared.. :x