I have a 14 year old pond that has worked well. Last year it was perfect! Clear water, healthy fish and beautiful water lillies all summer. But this year it is a mess. Very overgrown, muddy, no fish ( perhaps heron got them or else they are dead at the bottom), very few flowers on the lillies and they are all speckled with what looks like grey dust…..and worst of all lots of bluebottles! Should I empty it and start again? I have no pumps or filters.