The link I posted discusses the liner situation/and or brick/concrete base which can create problems of it's own. Just out of curiousity, what kind of fish do you have? How long have you had them? Did you make your own pond or was it professionally done? If you paid someone to do it, they should know what to do about your situation and so should the folks where you bought your fish from....I think the fish folks would be your best bet...give them a call!

Michelle