This is something we hear more often as more and more homes are being sold with ponds already built. Don't blame the former residents of the house. Ponds do not come equipped with an instruction sheet.
Every pond is different and there's no universal system.
Like pools, ponds can either add value to your property or become a deterrent when trying to sell. Ponds have a way of capturing the soul and many times a pond will help secure the sell of the home when it's up and running properly. If you are trying to sell your home make sure the pond is at its best when it's being seen. If you can, take time to show the new owner how the pond works and let him know what to expect. One of the best transitions of pond ownership I've seen involved giving our telephone number to the new residents.