Originally Posted by
mplskoi
I agree w Batman on 2 by 4's being plenty.
If it were me I would put one every 3 feet. Use two 3 1/2 inch deck screws to attach to the top. At 3 feet space they will be very handy to set racks/trays/shelves on. Might be a nice play to set your "starter" trays for plants.
Re: filtration- I (like ICU2) think a SG filter would be great for this application. I would set it on a very firm (cinder block) stand- it will weight over 400 pounds when in use. Set it so that the exit pipe comes out maybe 20-24 inches above pond height. You can then build a very simple "shower filter" so that the water comes out of SG and then hits the shower. The shower can be a simple tote bin from any big box store. Something about the size of a bushel basket. It can sit on these 2 by 4 cross members and fall back into pond from there.
There is a submersible pump that has multi speed function available at Home Depot. Think it is called the Eco Twist. You can dial it down to super low speed, or crank it up to full power and literally adjust it one watt at a time to find the perfect speed for your application. Consider setting this pump on the far end of the pond from filtration. Connect it via 2 inch PVC pipe painted black so it isn't visible in pond. Pump the water back to the filter end within the pond (no risk of hitting it with a shovel or wheelbarrow and causing external leak). Then have the water come out, up and over to SG filter.
Good pond design allows you to easily check for leaks and minimize what can happen if you do get one. Keeping the return line within the pond eliminates a few leak places. (or if it does leak inside the pond it wont matter).