Question
I have an old concrete 4 x 3 metre fishpond.  I've cleaned it out and want to repair cracks caused by age and root penetration cracking the surface.  What sealant should I use that won't harm the fish?  Do I need to reconcrete any larger holes first?  etc.
thank you for any advice you can give.  Also, as I'm in Australia, availability of some products may be difficult.

Answer
Hello Trude!
There are compounds available to seal concrete ponds, but I am afraid they are not of much use with wide-spread damage and none of them (that I know of) have any kind of warranty that they will totally fix the problem and/or keep it from recurring.
I my opinion you will be much better of using the current concrete pond as a shell and lining it with EPDM pond liner (available in large sheets).
That will solve the problem once and for all. It is very durable (be sure to use at least 45 mil thickness) and relatively easy to work with.
Best regards
Brigitte/www.pondmarket.com