On Sat, 18 Aug 2007 18:42:46 CST, RG wrote:

I'm about to expand my 400 gallon pond to a 1250 gallon. Yea!

Yea! :-)

Biggest question: Any tips, suggestions, opinions about joining a new
liner to the old one? Anyone have success doing this, or should I
just spend the $ on a new huge liner? (Don't forget, the "C" shape
makes for a lot of unavoidable bunching-up of liner, whereas is I join
the old to the new, I can avoid alot of the bunching).

Don't do it, buy one piece, even if you get it right, it will always be a
source of worry. So far I've yet to hear of a success story that I
remember.

Should I keep the old pump/filter set and get another 'small' filter/
pump set (and use both at once), or scrap the old and get one larger
new set?

Keep the old, but get a new larger one. The old is already cycled...
assuming you're going to some how keep it running during the remodel?
Perhaps on the holding container? ~ jan
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Zone 7a, SE Washington State
Ponds: www.jjspond.us