You probably know what you want, but I would like to comment on my experience with a pre-formed pond. I think mine was a 100 gallon. It had a recirculating pump/filter that had to be submerged in the pond to work. It took up a lot of space, not leaving a heck of a lot of room for a couple of fish. Digging a hole for a pre-form is a pain, because you can't get the shape that accurate, and getting the tub level is not an easy task either. Then you usually only have a depth of about 11"; not enough to protect your fish (if you plan on having fish) from predators. Small ponds are also pretty difficult to keep clean; well actually so are the big ones (at least mine is). My point is, that everyone thinks the pre-formed pond will save them work. In fact, I think it is easier to use pond liner. You get exactly what you want (shape and depth). But if that is what you want; Home Depot is where I got mine. We used it for about 2 years then dug a bigger pond with a liner. We love the pond, but it is easily 20 times more work than the railroad! I'm guessing if we ever did another one, it wouldn't be as much work, because we would use better equipment. End of rambling.
edit: And if you want pond liner, go on-line. MUCH cheaper, even with shipping.
I agree, Home Depot does carry a nice supply. I also purchased a very large one at a local Lowes store. If I'm not mistaken, I think it's just over 200 gal. We also have fish in it, and they have over wintered just fine in the mid-Atlantic region.
If you pre-level the base with sandand then back fill in behind the ponds walls WHILE you fill the pond, you should have no problems. I have a 60 gal preformed pond near my front door which has been there for about seven years. I've actually dug it up twice and relocated it on the layout because I've changed the layout's design. They are extremely sturdy. Mine is about 19" deep and I have wintered over goldfish in it. I bought it at Home Depot. I have also seen some nice designs at Lowes.
I'm not really excited about the pond liner as I've tried those before. My experience with them was not as good as the preformed, at least for a small pond, ~100 gallons. The issues I had were,:
- with a small pond the curves are tighter and the liner bunches up and doesn't look so good. Even after I put in flagstone overhanging the edge I could still see the bunched up areas.
- the bunched up areas around the tight curves also seem to hide more algea
- the algea seems to stick to the pond liners a lot better than the preformed, and was a lot harder to clean off.
A trick I learned for a guy who installs them professionally is to lay down an old piece of carpet . Keeps rocks and other things from poking holes in it.