I'd be wary of the weeds, until I knew what they were. They could end up
choking your VF. Remember, you want lots of plants in the VF, but you prefer
densely rooted plants.

LOL These weeds are very deeply rooted. The tops fall over into the
water, and new plants sprout from the seed heads...found this out
after hubby had weed-eated partially around the pond and the weeds
were left in the water... gads!

You may want to consider using lighter weight bio media, such as the stuff
that is commercially available. It'll cost you more, but save your back. I
am currently planning a trickle tower to be added to my VF, and when I do
it, I plan to use cross sections of PVC pipe. It'll be cheap. Easy to make,
and lightweight.

bio media instead of lava rocks?