Typically 2-5 turns per day are recomended, however, for what you are doing I would not be concerned so much with how many times you are turning the water. There are so many other variables to consider when constructing a waterfall for function as well as aesthetics. When applying the principles to achieve your desired results typically you will exceed the recommended tpd. As you can see from the photo above there is not enough aeration going on there to be adequate for the size of feature your are looking at building. I always tell my customers to go with the biggest pump they can afford. Not only the purchase price but also the monthly expense for operation. Design your system so you draw water from the bottom 1/3 of the column but not on the bottom and have your pump on the opposite side of the feature as your waterfall to keep the water circulated. Also when designing your waterfall keep aeration in mind. Instead of spreading the falls out like the above photo use narrow streams that run quickly over rocks churning the water and increasing the d.o. have several of these streams running into your bow and entering the bow at different locations but not directly over the pump. Then as part of the waterfall have a rock extending out at a high point and let the water fall from it 6 feet onto boulders at the bottom. Using this combination will optimize the d.o. from the waterfall. Keep in mind running water errodes so use a liner for your streams and your falls. Also get creative and use longer runs in your streams but keep them fast and churning.