Problem we have, fish dying: Goldfish kept in L-shaped feature pond and lined with 3 - 4 inch granite stones. 5 champagne fountains only aeration method for 3,600 Litre fresh water which is cycled thru a swimming pool filter (only Papyrus roots in contact with water) Fish fed with commercial feed. Owner ONLY wants to see live fish and the stones on bottom. Is this Possible? Owner believes that the nutrients have been taken out by the new filter which was upgraded because the fountain was blocking up.