submitted that Pat wrote:
A few months ago we applied a 'pond sealer' as our concrete based pond had
sprung a leak.
Since then all has been fine with the fish & no leaking. They have even
spawned & we have young goldfish (fanatails & shebunkins) thriving in a
seperate area.
All the plants that we had previously were vigorous & needed constant
cutting back but have now died.

Not a pond person but I keep planted aquaria and am constantly dosing
them with one nutrient or another. Do you suppose that the leaky pond
obtained some nutrients from the surrounding soil, and that
water-topping-off to compensate for leaks also added elements that the
plants liked? If so, water tests for macronutrients and addition of
lacking nutrients might help - don't forget the trace elements.
d.

Good catch D. I didn't even think about why it might have all worked in the
old pond and now isn't in the new. It all comes down to water parameters.
Hopefully Pat has some test kits. ~ jan