I think you have to be mad to run a big pond if you are on a water meter. Mine consumed tons of water per year. And if you aren't on a meter then they charge you extra per year for a pond.
I assume that's trickling of water through the pond to part exchange? The new pond should, once built, be using anoxic so in theory should gas off the nitrogen rather than end the nitrogen cycle at Nitrate that needs to then be either absorbed by plants (less likely) or removed by water exchange.