If anyone else is interested in assembling spawning structure,

I can share links but I found the cheapest 3/8" stainless threaded rod on Amazon. A 36" length was just about right and it was shipped for $6.55 each stick.

I then added rubber washers with 1/8" thickness but can be compressed, 1" diameter wide, 1/4" hole which stretches over the 3/8" and locks itself pretty well on the threads pinning the CDS in place. The CD hole is just over 1/2" diameter. ($9.50 for 100 pcs)

I then tried some black blank CD-R to see if color matters. Would be cheaper to get 'art project' Cds from ebay which I assume are recycled already recorded ones in random colors.

I added a nut top and bottom and on one rod put a combination of my left over silver CDs alternating with black, and on the other rod did all black to see if we see a difference. I can adjust the gap between the CDs by how much pressure I add with the nut on the top vs the nut on the bottom. Worked pretty well.

I had a nut with a round 'cap' on it that happened to fit so added one of those to the top of each rod so that when I pounded it in I was pounding on the top nut and not the threads.

The 3/8" rod is nice and stout for driving it in the pond bottom. Last time I used 1/4" zinc coated and it was a bit more bendy.

Aimed for about 18" under the stack of CDs as hope water will come up a few inches yet.