This is fun! The only reason water flows into the filter from the pond via gravity is because the pump is pumping water out of the filter. This system isn't a vacuum per say. The filter or settlement chamber has an open top. Water ALWAYS finds its level. If the system was closed the yes it would be the pump creating the the flow. If I were to shut off one of the filter pumps the water would stop moving to the filter. If then I were to open one of the cleanout valves at the bottom of the settlement chamber and let the water flow out freely to the ground then the water would start flowing again from the pond to the filter and out. Yes, I would be losing water, but the water would be exiting the pond at the same rate it was exiting the settlement chamber until the pond water level reached the same level as the entry into the settlement chamber. There isn't a pump moving that water, it is... gravity. The only purpose the pump serves is to be that 'open valve' and send water back to the pond. We are talking about koi ponds right? Just to make sure we are on the same page. The most popular pond for koi is a bare liner pond. As stated earlier it IS unnatural. That is why there are biofilters. And no need to approximate good quality water, there are lots of tests you can run to make sure you have good quality water. I don't understand the need for other living things in the water. Some of the best show koi are shown in bare liner ponds. It does act as the biofiltration. You wouldn't have biofiltration without it. What exactly does this mean? What Bbentler, if he has even looked at this thread lately, is asking for is something that is easier to maintain. Bare liner pond with bottom drain, in my opinion, is easier to maintain. No cleanout whatsoever.