Pre-form sagging / breaking? under weight of gravel

[Julles]

I have a mini bog set up in a very small preform spillway from Lowe's.  It's sitting up on a milk crate in the pond, and has about 100-200 lbs of gravel in it, plus plants. 

Well, I was wondering why the gravel level kept lowering, even though no one has taken any gravel out.  One side of the preform has gotten so low, the water is about ready to pour over the edge, instead of the spillway.

Today I discovered that the edges and parts of the preform that are not directly supported by the milk crate have been "melting" over the edges, sagging down under the weight of the gravel. 

I know plastic is maleable and stretchy, but I sure hope it has a high breaking point, 'cause I don't want a leak - or to have all that gravel and silt spill into my pristing pond. 

More stuff to buy:  Milk crates from Wal-Mart ... they have a rectagonal one that will fit under the preform. 
More stuff to do:  Empty bog and move 200lbs of gravel, and reset it up on the new crates.

[Ky Kim]

Have you ever see the things that stores use for 2 liter soft drinks.  Their really durable.  I use them alot when I need to get a pot a little higher in the water.  Might stop at a couple corner stores and ask if you could have a couple to try.  You could always spray paint them.

Kim

[Julles]

Now I'm thinking of moving the whole thing out of the pond, where the spillway will hang just enough to flow into the pond.

Need to think it through some more....

[Desertponder]

Wow, I doubt that will hold. You need to get the whole bottom of it on a solid surface, either outside the pond on the ground or something solid underneath the whole unit. Even still it may start bowing out on the sides. I've had preforms warp out of shape just from the weight of the water in them. I would think gravel would really do a number on one.