In article , "john hamilton" wrote:
I want to make a tray to contain a thin layer gravel that will lift out of
an acquarium.

I thought I would use a plastic box lid cut down to size and with square
section strips of wood screwed to each of the edges to form a lip to keep
the gravel contained.

Why wood? Why not something that's inherently waterproof? Rigid plastic such
as plexiglass would be a much better choice. So would any metal that's not
corroded by water contact, such as aluminum or brass. I think my first choice
for this project would be 1/2" aluminum angle, which you can find quite
cheaply at most hardware stores and home centers.

Or since you're cutting your plastic box lid down to size anyway, cut it about
an inch oversize. Heat it with a heat gun or a hair dryer and use pliers to
bent the edges up to form a half-inch lip all the way around.

Since the wood will permanently be under water ( that's fresh not salt
water) would ordinary pine be alright to use

Nope. It'll rot. Almost any wood will, if you leave it immersed in water long
enough. Some will rot faster than others, and pine will be one of the fastest.

(since this is what I have
already), or would I be best getting some kind of hard wood edging to make
this tray more durable over the long term? Thanks for advice.

For continuous immersion, if you insist on using wood, you really need either
lignum vitae or ipe. You might get away with redwood. But the other materials
mentioned above are vastly better, and don't run the risk of leaching anything
into the water that might be harmful to your fish.