Easy there bucko! If you'd like to have an educated discussion on how the decomposition cycle works in pond, we can do that. If the LINER pond is completely covered in about 12" or more of 'earth', then the somewhat natural earthen pond should provide the material needed to complete the cycle on its own. Again, stocking density is key. If you can maintain the proper balance of baitfish and predatory fish and keep the stocking levels monitored, you should be alright. Even with true earthen ponds, some commercial farms will use some type of roller or excavator to turn up the pond bottom every year or every few years. This makes sure that all the organic matter is receiving enough oxygen and does not turn anaerobic (stinky and rotten). Make sure your oxygen/air diffusers are placed at the bottom of the pond to turn over the entire water column. Once the balance that tadpole was talking about is achieved, don't sell or let the homeowner dump any 'pond clear' or some algae removal sludge. It will take care of itself!