That's a novel approach. UGF's in aquariums though, rely on a plenum that's under the entire substrate. I wonder about the ability of the airlift method you are using to draw water through the gravel and up into the planted area. I think what will happen is that there will be a small amount of water flow through the area that's closest to the airlift, and that's it. Plus you have the pipes spread out every 6 feet or so. The substrate between the pipes will still accumulate detritus. The new measurements do reduce the total gallon volume of your pond, but what's required for long term success is enough water circulation so that detritus doesn't have a chance to accumulate and can be in suspension until removed by mechanical means. Sand filters are designed to remove fine particles from swimming pools, not the larger debris associated with ponds that have plants and wildlife. Your pond volume is still 31,000 gallons. You need about 10 times your current water flow to deal with settling detritus, and that's if we can find an effective water circulation pattern. What are your long term plans for the pond? At this point I think it's going to be a lot of work and expense to design your pond with sufficient water circulation and filtration so that it will be successful in the long term. Depending on how much organic debris gets blown into the pond during the year, and from my experience, I think you will be dealing with an uncontrollable nuisance algae problem within 3 years and will be looking to disassemble the pond. Sorry, I wish I had a more optimistic opinion for you.